Articles (2020)

Introduction

During hard exertion, the body can produce sweat faster than it can evaporate. Liquid sweat begins to collect on the skin, and clothing must move that water away from the body through one or more layers.

A few months ago, I evaluated three base-layer garments and found clear performance differences. But one key question remained unanswered:

Which fabrics are most effective at moving liquid sweat away from the skin and into the next layer?

To answer that question, I developed a test specifically designed to track liquid water as it moves through a simplified clothing system. The test measures how much water remains on the “skin,” how much is retained in the base layer, and how much reaches the layer above.

In other words, it answers a simple but previously unmeasured question:

When skin is wet, where does the water actually go?

Figure 1 shows the test device used in this study.

As testing progressed, I expanded the scope from three fabrics to eight, representing a broader range of base-layer designs. With that expanded set, consistent patterns began to emerge.

The testing reveals several key patterns:

• Hydrophobic fabrics require sufficient pressure to initiate liquid transfer through their pore structure
• Pore structure strongly influences how effectively hydrophobic fabrics move liquid once transfer begins
• Hydrophilic fabrics rapidly absorb liquid from the skin but do not necessarily release it easily. Transfer depends on sufficient driving forces   –  primarily the pressure between layers and the receiving layer’s ability to draw in water. As the receiving layer becomes wetter, that ability decreases, reducing transfer. This behavior contrasts with the common expectation that wicking fabrics continuously move moisture away from the skin.

Together, these behaviors help explain a common experience: two garments may both be marketed as “moisture managing,” yet behave very differently once sweat becomes liquid. Some continue to move water away from the skin, while others become saturated and uncomfortable.

This article focuses on understanding why that happens. By tracking liquid water as it moves  – or fails to move  – between layers, the testing provides a clearer picture of how base-layer fabrics behave under high-exertion conditions.

How to Read This Article:

This article does three things:

1. Introduces a new test method,
2. Explains the physics of hydrophobic vs hydrophilic behavior, and
3. Presents experimental results.

That is a lot, but you will learn a lot about how base layers function.

If you want a quick takeaway read:

• How Hydrophobic and Hydrophilic Fabrics Transfer Liquid Moisture
• Case 1 Results
• Conclusions

For a deeper understanding, read the full text. The appendices provide additional detail. Alternatively, read a section or two at a time and then come back to it. There is a lot here, but I think these tests raise the bar on our insights into how base layers work.

Author’s Note:
The results and conclusions presented here apply to the eight fabrics tested in this study. I do not claim that these findings extend to all hydrophobic or hydrophilic base-layer fabrics. However, the observed behaviors are consistent with well-established physical principles described in the scientific literature, beginning with Young and Laplace (1805) and later formalized by Washburn (1921). These foundational studies describe the capillary physics that underpin modern understanding of liquid transport in fibrous materials.

How Hydrophobic and Hydrophilic Fabrics Transfer Liquid Moisture

Hydrophobic fabrics can get wet, and they can transfer water effectively

Hydrophobic base layers are often described as “staying dry,” and in one narrow sense, that’s true   –  the fibers themselves do not attract or absorb water. But during hard exertion, many hikers have experienced something that seems to contradict this idea: hydrophobic layers can feel heavy, clammy, and very wet.

The reason is simple but often overlooked. Fabrics are mostly empty space. Even when the fibers repel water, liquid sweat can still collect inside those empty spaces. In other words, a hydrophobic garment can hold a surprising amount of liquid water without the fibers ever becoming “wet.”

Figure 2 shows this clearly. After high-intensity activity in cold conditions, large amounts of liquid water can be seen within two hydrophobic garments. In the infrared images, darker blue regions indicate areas of high water content. Despite being made from hydrophobic fibers, both garments contain substantial amounts of trapped liquid sweat. The Brynje mesh shirt (right) retained 87 g of sweat (65% of its dry weight), while the Alpha Direct shirt trapped 62 g (55% of dry weight).

Whether a hydrophobic garment stays relatively dry or becomes saturated depends on a simple balance: how fast liquid sweat enters the fabric versus how quickly it can move through and out. If liquid water passes through the fabric as fast as it arrives, little accumulates. If transfer is slower than incoming sweat, liquid gradually fills the pore spaces, and the garment becomes increasingly wet  – even though the fibers remain hydrophobic. In that condition, the fabric may feel clammy, heavy, and provide reduced insulation.

In my testing, hydrophobic fabrics do not absorb water through capillary action. That distinction is important. Capillary-driven uptake occurs when fibers attract water molecules to their hydrogen bonding sites. True hydrophobic fibers lack these bonding sites and therefore cannot generally pull water into the fabric on their own.

Instead, hydrophobic fabrics require external pressure to force liquid water into their pore structure. If available pressures are too low, a hydrophobic fabric can act like a water barrier. As pressure increases, that same fabric may suddenly begin to pass water through.

There is a minimum pressure required to force water into the pores of a hydrophobic fabric. The classic work of Laplace and Washburn, cited above, describes how this pressure can be calculated for a single capillary. I’ll refer to this threshold as the breakthrough pressure.

In real use, this pressure can come from many sources: compression from outer layers or pack straps, movement of the body against clothing, tension in tight-fitting garments, friction between layers, or simply the weight of accumulating liquid sweat. Sliding, stretching, and rubbing can generate brief, localized pressures that momentarily force water into pore openings. Until that pressure threshold is reached, water may remain pooled on the skin.

What determines how much pressure is required? According to Laplace and Washburn (cited above), breakthrough pressure depends largely on two factors: the size of the pore opening and the contact angle between water and the fiber surface. There are other factors that influence breakthrough pressure in a fabric, but, as we shall see, our calculations based on pore-opening size and estimated contact angle correlate well with actual fabric performance.

My testing confirmed that the largest pore openings corresponded to reduced breakthrough pressure. Smaller openings require more pressure to force water through them. At the same time, my testing showed that the breakthrough pressure increased with a higher contact angle.

What is Contact Angle?

Contact angle is a measure of a fiber’s resistance to water. It is measured by how a water droplet sits on a fabric surface. When a water drop deposited on a fabric surface spreads out to form a flattened drop, the surface is hydrophilic and supports capillary wicking. When a water drop beads up into a tall dome, the surface is hydrophobic and resists wetting. Contact angles below about 90° show hydrophilic behavior, while angles above 90° indicate hydrophobic or water-repellent behavior. Many hydrophobic base layers fall in the range of roughly 95° to 115°, whereas strongly hydrophilic materials may exhibit very low angles, approaching zero.

Pore Size and Pathways

It is important to note that apparent pore size alone (measured under the microscope) does not determine how easily liquid passes through. The actual pathways inside a textile are three-dimensional and often constricted where yarns cross or partially block pathways. As a result, fabrics that look very open can still resist breakthrough, while others with smaller visible openings may allow flow if their internal pathways are better connected.

This framework helps explain why hydrophobic base layers behaved so differently in the tests  – and why they may behave differently in real use. One fabric may transfer sweat efficiently and feel relatively dry during intense activity, while another may allow sweat to accumulate on the skin or within the fabric, leading to discomfort  – even though both are made from water-repellent fibers.

Key Takeaways:

1) Hydrophobic fabrics can become wet due to water stored in open pores.

2) In this test, hydrophobic fabrics do not transfer sweat until sufficient pressure forces water into their pore structure.

3) Both pore structure and fiber chemistry greatly influence the pressure required to initiate flow.

4) If water enters a hydrophobic base layer’s pores faster than it leaves, the fabric will retain water and become wet.

Hydrophilic Fabrics: Familiar Strengths, Important Limits

Hydrophilic base layers behave as most hikers already recognize. When liquid sweat appears, these fabrics absorb it immediately, pulling moisture off the skin and spreading it through the fiber and yarn structure by capillary action. This behavior – often described as “wicking” – is discussed in detail in earlier articles, Why Is My Wicking Layer Wet? and How Do Moisture-Wicking Fabrics Work? , which I won’t repeat here.

What matters for this article is a less intuitive point: the same capillary forces that make hydrophilic fabrics absorb sweat so readily also make them inclined to hold on to it.

In a hydrophilic fabric, liquid water is drawn into the pores and distributed through the fabric structure by capillary forces. Once absorbed, that water is not free to move unless another force acts on it. Transferring liquid water to the next layer, therefore, results in a competition between the base layer’s tendency to retain water and the receiving layer’s ability to draw it away.

When the receiving layer is dry, it can readily draw water from the base layer. But as the receiving layer accumulates moisture, its ability to pull additional water decreases. As a result, liquid transfer can slow dramatically  – or stop altogether  – even while the base layer remains wet.

I observed this behavior across all experiments conducted for this article. In two tests, the receiving layer water absorption capacity was reduced in different ways. In each case, less water was transferred from the hydrophilic base layer to the receiving layer. In these tests, the performance of hydrophobic fabrics was largely unchanged and exceeded that of the hydrophilic samples. In two other tests, the hydrophilic base layers simply transferred less water than the hydrophobic samples (with two hydrophobic exceptions). These results are explored in detail in the results section.

Development of my Water Transfer Test Device

Measuring Liquid Transfer Between Clothing Layers

A critical function of a base layer is to facilitate the transfer of liquid water from the skin to the next layer. However, conventional fabric tests have not been developed to assess how well base layers hand off liquid sweat once skin becomes wet. Existing tests typically focus on absorption, vertical wicking, or vapor transmission in single layers. None directly answers a simple question:

When skin is wet, where does the water actually go?

To address that gap, I developed a simple test designed specifically to measure liquid water transfer between clothing layers. The test tracks how a known quantity of liquid water is distributed after contact with a base layer and a receiving layer under controlled pressure.

The test measures three outcomes:

• How much water remains on the “skin”?
• How much is retained in the base layer?
• How much is transferred to the receiving layer above?

The primary measure of success is the amount of water transferred to the receiving layer. However, the location of any untransferred water is also important, because water remaining on the skin and water trapped within the base layer have different implications for comfort and insulation.

The test is intentionally simplified to isolate liquid transfer between layers. It does not attempt to measure vapor transport or evaporation. It does not consider what happens when sweat remains primarily in vapor form. Instead, it focuses narrowly on what happens once sweat has already condensed into liquid and must be moved away from the skin.

Water Transfer Device Configuration and Use Description

1. A skin layer is attached to an acrylic plate. This is the bottom of the stack.
2. A measured water dose is applied to the skin layer.
3. The base layer is placed on the wet skin surface.
4. The Receiving layer is placed on the base layer.
5. A weighted acrylic platen is placed on the Receiving layer.
6. Prior to the test, I weigh the dry skin plate, the water-dosed skin plate, the base layer, and the Receiving layer. Measurements are recorded to .01 grams.
7. The test runs for two minutes.
8. At the conclusion of the test, I reweigh each layer.
9. I then calculate the water gain in the receiving layer, the base-layer water retention, and the water remaining on the skin layer.

The mark of success is the amount of water transferred to the receiving layer. But where the untransferred water remains has important implications for your comfort: whether water is in the base layer or on your skin. The test reveals all three outcomes.

Test Process Decisions

In developing the test, it was important to select suitable materials for the skin and receiving layers. I started with a hydrophilic skin material but found that it resisted releasing its water content, even when weighted. The pressure from the weighted platen could not overcome the capillary forces of the hydrophilic skin material. Using a hydrophilic skin is not appropriate because human skin is mildly hydrophobic, with a contact angle ranging from 70° to 100°. After testing several options, I ultimately chose a lightly textured hydrophobic film.

The skin layer approximates wet skin only in a narrow sense: it provides a mildly water-repellent, non-absorbing surface from which liquid water must be removed. It does not simulate sweat gland distribution, skin compliance, salt content, skin oils, hair, body heat, or continuous sweat production. Results should therefore be interpreted as a controlled liquid-transfer comparison, not a full physiological simulation of sweating skin.

The receiving layer consists of two-ply paper towels. At skin doses of 5 grams, I used a single layer of paper towel. For doses of 10 and 15 grams, I used two layers. A single layer of paper towel could hold over 15 grams of water. This choice allowed me to accommodate expected water doses without restriction.

The receiving layer is not intended to represent all possible outer layers. It functions as a standardized absorbent sink. Therefore, these results compare how each base-layer fabric transfers liquid water into this specific receiving medium under controlled pressure. Different receiving layers – especially hydrophobic, low-absorbency, lofted, or highly air-permeable layers – may produce different transfer rankings.

The pressure exerted by the body or clothes on a base layer is not well documented. There are some sources, such as compression clothing, but these exert too much pressure. For initial testing, I set the pressure to 0.3 kPa. I also tested at 0.1 kPa. I found similar results for both pressures. However, 0.1 kPa is probably a better value to use for future testing. It helps identify hydrophobic fabrics that don’t perform well at realistic pressures.

The applied pressures should be interpreted as controlled screening pressures rather than precise simulations of clothing pressure on the body. Real use likely involves lower average pressures combined with brief localized pressure spikes from movement, pack straps, garment tension, and body contact. These intermittent events may be especially important for hydrophobic fabrics because they can initiate breakthroughs.

The following photographs illustrate the device components and some use cases.

Test Limitations are discussed further in Appendix 1.

Fabrics Tested

I selected a total of eight fabrics for this project. Three were provided by Finetrack (as shirts). These are the latest versions of their Elemental Layer products: Cool, Basic, and Warm. Basic is the Elemental layer they have been selling for years. Cool and Warm are new products. These are thin, light, and highly hydrophobic products with differing pore openings. I added three hydrophobic base layers: Brynje Super Thermo, Gore Base Layer, and Helly Hansen Lifa 48300. I also included two hydrophilic base layer fabrics: Polartec PowerDry Silk Weight and Polartec Delta.

These materials vary in thickness, yarn geometry, pore openness, and fiber chemistry. Together, they provide a broad spectrum for evaluating the performance of thin, lightweight base layers.

Let’s first see what these fabrics look like. Figures 6 and 7 show photomicrographs of our eight fabrics. For a clearer view, I encourage you to zoom on the images.

Figure 6: PowerDry Silk Weight, Finetrack Cool, Finetrack Basic, Finetrack Warm.

Figure 7: Brynje Super Thermo, Gore Base, Lifa 48300 and Polartec Delta.

What clearly distinguishes these fabrics is the size of the openings they provide. We will see that large pores and large numbers of large pores will be critical for liquid transfer in hydrophobic base layers. You can simply look at these and get a good idea of which will be the star performers.

Baseline Fabric Properties

For my first analytical step, I undertook the standard test procedures that I have developed over time. I added some new measurements that I thought would shed light on liquid transfer performance. I then produced a Baseline Fabric Properties table that focused on liquid transfer performance. This data shows how the fabrics differ in key physical properties. As we will see, these properties hint at, but do not predict, liquid water transfer performance. We will get to that in the next section.

I present a short version of the Fabric Properties in Table 1 and then describe some relevant performance highlights. For data nerds, the complete Fabric Properties table and full comments are in Appendix 3.

Table 1: Key Fabric Properties

Now, a brief discussion of key points.

Fabric Thickness

As noted in previous articles, the amount of moisture a fabric holds at saturation and the energy required to dry it increase with thickness. This trend generally applies to our samples, except for one fabric pair that switches the ranking of saturation water (Warm and Deltas). The thickest yarns are in Brynje, and they hold the most water and require the most energy to dry.

Yarn Diameter

This measurement can provide limited information about how much water may be trapped in yarns, with thicker yarns tending to trap more water. The thickest yarns are found in Brynje, which also traps the most water.

Water Repellency

This test shows whether the fabric is hydrophobic (phobic) or hydrophilic (philic).

Optical Porosity

This is measured under a microscope. Since I select two parameters to complete the measurement in Photoshop, the measurements are somewhat subjective. This measurement identifies direct paths through the fabric where light-and potentially liquid or vapor  – can pass. It provides important insights into how easily water or vapor can transfer through a fabric. Of course, Brynje stands out from all other fabrics in this measurement. The new Cool fabric also shows very high porosity. This measurement is more important for hydrophobic fabrics. Hydrophilic fabrics don’t need large pore sizes to transfer liquid water.

Air Permeability

This is another measure that indicates how readily liquid water or vapor can move through a fabric, particularly a hydrophobic one. One must be cautious with this measurement. It is made under relatively high air pressure, which can distort the size of the fabric openings. Vapor and liquid transfer in a fabric may deviate from the data provided by the test results. In general, we expect fabrics with higher air permeability to have more and larger direct paths through the fabric. Again, this will be more important for hydrophobic fabrics than hydrophilic fabrics.

Void Fraction

I include this new measurement because I think people don’t appreciate how much air is in a fabric. In fact, a very small fraction of the volume of a fabric is fiber, and most of the volume is air. In this group of fibers, at best 19% of the volume is fiber, and the rest is air! The more air in a fabric, the greater its potential to trap insulating air- provided that air is not free to circulate. More trapped air means more warmth. Not surprisingly, Brynje has the highest Void Fraction and the highest R-value. Warm has the 2nd highest Void Fraction and the 2nd highest R-value.

Thermal resistance

The thermal resistance of a base layer is usually negligible compared to that of the additional layers worn in cold weather. I do not typically measure it, but I did so here because some manufacturers claim their base layers are better suited for cold conditions or provide greater warmth than other fabrics.

I measured five of the eight fabrics. A fabric called Warm piqued my curiosity. In fact, Warm’s R-value is less than Basic and doesn’t stand out among the five fabrics tested. However, it does have lower air permeability and porosity than the other Elemental layer products. This may reduce convection losses, but it may also reduce Moisture Vapor Transmission Rates.

Brynje produces an R-value more than twice that of the other fabrics. This result relies on a large amount of still air “trapped” between the thick yarns, but in real use, convection caused by pumping of the outer layers and pressure from the user’s body would likely reduce that trapped air. I believe that in actual use, Brynje’s R-value would be smaller than what I measured. There’s a reason insulating fabrics use complex fiber distributions to prevent air from circulating within the insulation during use.

So, based on these key property measures, which base layer fabrics will provide the best water transfer away from the skin, through the base layer, and into the Receiving layer?

The baseline measurements alone do not answer that question. The next section presents the results from the new test device. This is where we will find the answer.

Water Transfer Test Results

I present the test results using three graphs for each of three test cases. A fourth case is presented in six graphs. In each case, one parameter  – skin dosing, receiving-layer dosing, receiver layer capacity, or platen pressure  – is varied while the others are held constant.

I explain the graphs in detail for the first case and then summarize the key findings for each case.

Case 1: Increased Skin Dosing

Skin Dosing: 5, 10, 15 grams; Platen Weight: .31 kPa; 8 Fabrics

Figure 8 presents the results for Case 1 using three graphs. The top graph shows water transferred to the receiving layer, which is the primary measure of success in this test. The higher the bar, the better the performance. Simple! The middle graph shows water retained in the base layer, and the bottom graph shows water remaining on the skin. Lower values in the middle and bottom graphs indicate better performance.

There are three iterations of this test, with 5, 10, and 15 grams of water added to the skin, as shown on the x-axis. Performance is compared by the relative bar heights within each dosing level.

Water transferred to the receiving layer-Best and Worst Performance

The top graph shows that the relative performance of the fabrics changes little with increasing water dose. This indicates that, once liquid transfer is established, higher sweat rates can be accommodated provided the clothing system has sufficient capacity to move water through its layers. We can easily see the best and worst performers.

Across all dosing levels, Basic and Gore consistently transfer the most water to the receiving layer, followed closely by Cool. At the 10-gram dose, Basic and Cool are essentially tied. These fabrics show the most effective liquid transfer under the conditions tested.

At the opposite extreme, Warm transfers almost no water to the receiving layer across all doses. The bottom graph shows why: nearly all of the water remains on the skin. Liquid water does not penetrate Warm’s pore structure at the applied pressure, indicating a high breakthrough pressure.

What accounts for Warm’s high breakthrough pressure? Small pore sizes. The Laplace-Washburn formula, described earlier, explains how breakthrough pressure depends on pore size and contact angle. The formula illustrates that, at contact angles below 90°, capillary pressure draws water into the fabric. Above 90°, water is repelled from fabric capillaries and does not enter the fabric by means of capillary force.

Using the Young-Laplace formula, I calculated the breakthrough pressure for each of our hydrophobic fabrics. If readers are interested, the calculated breakthrough pressures are shown in Appendix 2. The calculated results correlate well with the test results, except for Brynje, which will be discussed below.

The contact angles for the hydrophobic fabrics appear similar, except for the Lifa fabric, which, from our Appendix 2 calculations, is slightly lower. Thus, we can simply examine the pore size of each hydrophobic fabric and infer which fabric has the highest breakthrough pressure.

You can easily do this. Go back to Figure 6. The right-most image is Warm. Zoom in as far as you can and look at the large pores in Warm. They are considerably smaller than all of the other hydrophobic fabrics. But their performance is even worse than it might appear. If you look closely at any of the large pores in Warm, you can see that they are subdivided by intersecting yarns. Thus, instead of one large pore, they behave like three or four much smaller pores. In my opinion, those yarns are the primary reason that Warm fails to transfer water from the skin in the test.

Middling Water Transfer Performers

Let’s examine two other lower performers in the Receiving Layer graph: the hydrophilic fabrics PowerDry and Delta. These two fabrics underperform compared to the hydrophobic fabrics, except Warm. Where is the water? If we look at the bottom graph, we don’t see any PowerDry (purple) or Delta (teal). That indicates they removed almost all water from the Skin Layer.

Now, let’s look at the middle graph: Fabric Water Retention. Here, the two hydrophilic fabrics retain more water than the other fabrics.

Why don’t these hydrophilic fabrics give up their water to the receiving layer?

In How Do Moisture Wicking Fabrics Work?, I described how capillary structure influences liquid movement. Tighter fiber spacing creates smaller diameter capillaries that generate higher capillary pressure and can move water farther. Larger diameter capillaries can hold more water but exert less capillary force. This is classical wicking behavior described by Washburn, cited above.

When two hydrophilic layers are in contact, both large and small pores are present at the interface. The larger pores in the base layer hold water less strongly and are drained first by the receiving layer. These can be thought of as “low-hanging fruit.”

As transfer continues, the remaining water is held in progressively smaller capillaries within the base layer, where capillary forces are higher. At that point, further transfer requires the receiving layer to exert a stronger capillary pull. As the receiving layer becomes wet, its ability to do this decreases. Eventually, the capillary forces in the two layers reach a balance, and transfer stops  – even though water remains in the base layer.

Why does PowerDry consistently transfer more water than Delta? Two factors likely contribute:

1. Pore structure and connectivity: PowerDry has relatively high optical porosity, meaning it has large, open pathways through the fabric. Water in these larger pores is held less strongly by the base layer and can be transferred more easily by the receiving layer. Delta has much lower optical porosity, with smaller pores and fewer unobstructed pathways. Water is held more strongly, and some of it may reside in poorly connected areas that do not readily drain into the receiving layer.
2. Thickness and path length: PowerDry is approximately 0.61 mm thick, while Delta is about 0.91 mm thick. The greater thickness of Delta increases the distance water must travel and provides more internal volume for storage, making it more difficult for the receiving layer to draw water all the way through the fabric.

We will see more of this effect in the cases that follow and also discuss its implications for real-world water transfer between wicking layers.

Special Case: Brynje

Brynje always comes in fourth on the Receiving layer chart. Brynje has two ways to pass water. If liquid water floods the large pores, water can contact the Receiving layer directly, thereby transporting large amounts of water. If the water does not overrun the large pores, it must travel through the thick yarns; this is a less efficient means of transfer. So, where is the water that did not transfer into the Receiving layer? We can see it in the middle chart: Fabric Water Retention. In every dosing case, the fourth-highest bar is Brynje. Part of the water is stuck in the yarns. This is a hydrophobic fabric, so the capillary balancing act we described above does not apply here. But I think some of the same issues are present: some pathways within the yarns are larger and require less water pressure to move large volumes of water through. Others are smaller or restricted and require more pressure than is available to produce water flows. So, water remains trapped in the yarns.

Case 2: Reduced Platen Pressure

Skin Dosing: 5grams; Platen Pressure: .31 kPa and .10 kPA; 8 Fabrics

In this case, I wanted to assess the fabrics’ performance at lower pressure to see how it compares with the test results we have already seen. The results are shown in the next set of graphs:

Each graph has two panes: the left is the results we saw for the 5-gram dose at 0.31 kPa. The right pane shows the results for the same test at a pressure of 0.10 kPa.

In the Receiving layer graph, the results for the two cases are nearly identical, except for Lifa. At 0.10 kPa, only 0.055 grams of water are transferred to the Receiving Layer. Most of the water remains on the Skin Layer, with the remainder in the fabric. The exact mechanism for this is unclear. But the results say the breakthrough pressure is between 0.10 kPa and 0.31 kPa. Appendix 2 provides a calculated value of .27 kPa, consistent with the test results. The actual value is probably somewhat lower.

Key Takeaway: Future testing should be conducted at .10 kPa to better identify hydrophobic fabrics unlikely to transfer sweat.

Case 3: Case 3 Decreased Receiver Layer Capacity by Water Dosing

Dosing-Skin Dosing: 10 grams; Platen Pressure: .31 kPa, Receiving Dosing: 0, 5, 10, 15 grams; 2 Fabrics

This test examines how reduced receiving layer water impacts water transfer performance. In this case, water capacity is reduced by adding increasing water doses to the receiving layer while holding skin dose and platen pressure constant.

In the receiving layer, the results are clear: For Basic, the hydrophobic fabric, water transfer is unaffected by the receiving layer water dosing level. Nearly the entire skin water dose is transferred. At sufficiently high dosing levels, transfer would likely decrease. I did not push the test that far.

In contrast, PowerDry, the hydrophilic fabric, shows a strong dependence on the water content of the receiving layer. Transfer occurs at 0 grams, decreases at 5 grams, and is effectively eliminated at 10 and 15 grams.

Where did the water go? In the Water Retention graph, we see that retention in the base layer increases from the 0-gram dose to the 5-gram dose and then stabilizes for the 10- and 15-gram doses. We see a modest increase in residual water on the skin layer as doses increase.

Key takeaway: As the receiving layer becomes wetter, its ability to draw additional liquid decreases. A point is reached where the Receiving layer can no longer overcome the capillary forces within the hydrophilic base layer, and transfer effectively stops. In contrast, the hydrophobic fabric remains largely unaffected over this range.

Case 4: Reduced Receiver Layer Capacity

Skin Dosing: 10 grams; Platen Pressure: .31 kPa, Receiving Layer 1 ply paper towel; 6 Fabrics

This test examines how reduced receiving layer capacity impacts water transfer performance. Receiver capacity was reduced by separating a 2-ply sheet and using a single ply. Capacity is reduced by 50% compared with Case 3 and 75% compared with the 10 gram skin dose of Case 1.

With reduced receiving layer capacity, water retention in the hydrophilic base layers increases substantially.

The transfer performance of the hydrophobic fabrics Basic and Cool is unchanged. Transfer performance for hydrophobic fabrics Brynje and Gore, showed modest changes. Brynje transfer increased by 1.5 grams while Gore decreased by a similar amount. The reason for the changes in these two fabrics is unclear.

Key takeaway: Reducing receiving layer capacity limits its ability to accept additional liquid, resulting in increased water retention in hydrophilic base layers. This effect is consistent across Cases 1, 3, and 4. In contrast, hydrophobic fabric performance was largely unchanged.

Conclusion

Which Fabrics Transfer The Most Water away from the skin? Here is a simple ranking under Cases 1 and 2.

Here is a brief review of what we have learned in this research:

Hydrophobic Fabrics

1. These fabrics can become wet by storing water within their structure.
2. These fabrics require some pressure to initiate and maintain water transfer from the skin, through the base layer, and into the receiving layer.
3. The pore structure strongly influences their ability to transport water.

Hydrophilic Fabrics

1. These fabrics can readily absorb water through contact with wet skin.
2. These fabrics may require some pressure to transfer water from the base layer to a hydrophilic receiving layer.
3. The exchange of water between hydrophilic layers is not constant, but changes as water accumulates in the receiving layer. The drier the receiving layer, the more strongly it pulls water from the base layer. As it becomes wetter, that pull weakens. Eventually, the driving force for transfer decreases until little or no additional water moves between them.

This work represents an initial effort to quantify how layered clothing systems transfer liquid water. Future work will expand on these findings and further explore how fabric structure and layering affect real-world performance. I look forward to your questions as we refine this testing approach.

Appendix 1: Test Limitations

In its current configuration, the liquid transfer device has a limited scope: it measures liquid transfer between a base layer and a receiving layer. Direct analogs applied to both hydrophobic and hydrophilic base layers appear to be absent from the textile research literature.

In practical layering systems, we select garments that allow sweat to move away from the skin and ultimately evaporate to the environment, which serves as the final “sink.” This test does not replicate the full pathway from skin to environment.

The current configuration ends with a receiving layer that serves as a simplified sink for liquid water. Future work will explore alternative sink materials, including hydrophobic receiving layers, and will extend testing to lower pressures and to different fabric combinations.

Another area for further study is the behavior of highly compressible fabrics. Fuzzy or lofted materials may undergo significant structural changes under load, potentially altering liquid transport behavior relative to in-use conditions.

Appendix 2: Laplace/Washburn Calculations

The capillary entry pressure can be estimated using the Laplace relationship:

\[

P_s = \frac{2\gamma}{r}\cos\theta

\]

Where:

Ps=Breakthrough Pressure
γ = surface tension of water (approximately .0728 N/m)
r = radius of the capillary, or in this case, a large pore
cosθ = Cosine of the contact angle of the fiber surface.

A contact angle less than 90° produces a positive value of cos cos θ, resulting in capillary suction. A contact angle greater than 90° produces a negative value, indicating resistance to liquid entry.

To calculate the capillary radius, I measured the area of typical large pores under the microscope and then calculated the equivalent radius that would produce that area.

Here are the results:

Notes:

Two results are shown for Warm. The first uses the total area of a large pore. Using the full pore area predicts penetration at 0.31 kPa, although no penetration is observed at that pressure. The second recalculates using the area of a smaller subpore formed by three yarns crossing the large pore. Using the area of a typical subpore reproduces the behavior observed in the water transfer test.

Initially, contact angles of 110o were assumed for all fabrics. Similar contact angles were used for most fabrics, with a lower value for Lifa to match observed behavior: penetration occurs at 0.31 kPa but not at 0.10 kPa. The calculated value of 0.27 kPa aligns with this observation.

Appendix 3: Complete Baseline Fabric Properties

Fabric Thickness

As noted in previous articles, the amount of moisture a fabric can retain and the energy required to dry a saturated garment increase with thickness. This trend generally holds for this sample, except for one fabric pair that reverses the ranking of saturation water (Warm and Deltas). The thickest yarns are in Brynje, and they hold the most water and require the most energy to dry.

Yarn Diameter

This measurement can provide limited information about how much water may be trapped in yarns, with fatter yarns tending to trap more water. The thickest yarns are found in Brynje, which also traps the most water.

Water Repellency

This test establishes whether the fabric is hydrophobic (phobic) or hydrophilic (philic). The results establish broad expectations for fabric performance.

Yarn Twist

This is a qualitative observation under the microscope. Less twist can mean higher yarn porosity, which can increase the amount of liquid held in the fabric. All but one fabric have no yarn twist. Finetrack Basic has very loose yarns that may increase its ability to hold moisture.

Saturation Water/Dry Fabric Weight (%)

This shows which fabrics, as a % of dry weight, can hold the most water. We can see that Basic has the highest water saturation content. This may be due to its very loose yarns. Brynje is not far behind with its very fat yarns. This test shows a fabric’s ability to hold water. This does not mean a fabric will ever hold that much water in normal use (short of falling into a steam). We will show that it appears to be a factor in our liquid transfer tests.

Water Removed by Wringing (%)

A colleague’s unpublished research on saturation indicates that the water remaining after hand-wringing a fabric is a more reliable indicator of how much water might be trapped in a fabric during use. This makes sense because wringing should remove surface and unbound water, which may drip more readily from a garment when worn.

Void Fraction

I include this new measurement because I think people don’t appreciate how much air is in a fabric. In fact, a very small fraction of a fabric’s volume is fiber, and most of the volume is air. In this group of fibers, at best 19% of the volume is fiber, and the rest is air! The more air in a fabric, the greater its potential to trap insulating air, provided that air is not free to circulate. More trapped air means more warmth. Not surprisingly, Brynje has the highest Void Fraction and the highest R-value. Warm has the 2nd highest Void Fraction and the 2nd highest R-value.

Water-Filled Void Fraction

This measure indicates the fraction of fabric volume filled with water at saturation. You may ask, “Why is Brynje so low?” The answer is that at saturation, water is confined to the yarns. It does not fill the large mesh voids.

Air Void at Saturation

If you take the total fabric volume, subtract the fiber volume and the saturation water volume, you are left with the void space that may be available for vapor or liquid transfer through the fabric. Of course, Brynje wins this by a wide margin. For most fabrics, you don’t know how torturous the path is that connects these air voids. The more tortuous, the less likely it is to support water or vapor transfer.

Saturation Drying Energy, Saturation Drying Rate

These align with what we expect from my prior drying articles. It typically requires about 1 wh/g to dry moisture from the fabrics, with small variations. Water typically dries at a rate of about 1 g/minute, with greater variation depending on fabric thickness or other structural characteristics.

Thermal resistance

The thermal resistance of a base layer is usually negligible compared to that of the additional layers worn in cold weather. I do not typically measure it, but I did so here because some manufacturers claim their base layers are better suited for cold conditions or provide greater warmth than other fabrics.

I measured five of the eight fabrics. A fabric called Warm piqued my curiosity. In fact, Warm’s R-value is less than Basic and doesn’t stand out among the five fabrics tested. However, it does have lower air permeability and porosity than the other Elemental layer products. This may reduce convection losses, but it may also reduce Moisture Vapor Transmission Rates.

Brynje produces an R-value more than twice that of the other fabrics. This result relies on a large amount of still air “trapped” between the thick yarns, but in real use, convection caused by pumping of the outer layers and pressure from the user’s body would likely reduce that trapped air. I believe that in actual use, Brynje’s R-value would be smaller than what I measured. There’s a reason insulating fabrics use complex fiber distributions to prevent air from circulating within the insulation during use.

So, based on these key property measures, which base layer fabrics will provide the best water transfer away from the skin, through the base layer, and into the Receiving layer?

MVTR

This measurement is not made. I assume that the MVTR of these fabrics is generally adequate to remove moderate amounts of vapor and that the greater barriers to vapor removal will be in the subsequent layers through which it must pass.

Related Content

• Gear Testing and Research: How Fishnet Works
• Gear Testing and Research: By the Numbers: Thermal Performance Measurements of Synthetic Insulations