By the Numbers: The Tug of Water – Why Some Layers Hold Sweat and Others Let it Go

Interesting analysis Stephen, though I’m not sure how to practically apply it yet. (maybe a couple more reads). For my purposes, I am more interested in having the sweat/moisture evaporate from my baselayer than pass into the next layer, and in practice, not the test lab, it seems in all cases thinner is better and loosely fitting (not baggy though) is better. I can’t wear synthetics so am limited to hydrophilic fibers. Processing…

Enjoyable read, thanks Stephen.

In field use, the Brynje doesn’t feel wet for me despite the thicker yarn retaining moisture.  This might be because so much of the surface is void so there’s far less skin contact with wet fiber than with a more homogeneous fabric that retains similar water weight.

This is a great showing for Brynje because once vapour transmission and a bit of air movement is factored in, total water transfer off skin for it will be much higher than for the tighter weaves, without a significant absorption penalty due to the thicker yarn.

Decades of using the Lifa line up with your results for me.  As a base layer, once its wet it likes to stay wet.  Mid layers usually aren’t tight so little pressure is exerted to pull water off the Lifa.

Where I find Lifa shines is acting as the receiving layer, as a lightweight mid.   I put it over the Brynje, and it pulls moisture away really well.  Air movement from activity and wind is usually more than enough to evaporate the moisture off it.  If I need a bit more warmth, I add a second highly breathable mid like an octa over the brynje/lifa combo and more than enough air usually gets through to keep skin and Lifa dry.  At long stops an Alpha 120 goes over and my body heat is enough to boil the water off the Lifa, I can see steam rising through the combo when its cold.

This article looks closely at how hydrophobic and hydrophilic base layers move sweat off the skin and transfer it to the next layer. The article demonstrates that hydrophobic and hydrophilic base layers use different processes to accomplish that task. It points out that transfers from hydrophilic base layers may be limited by the properties of the receiving hydrophilic layers. Your comments suggest that you only use natural base layers. I presume that means merino wool base layers. The behavior of a merino wool base layer will be heavily influenced by its processing. The cuticle layer covers the exterior of the merino wool fibers. The cuticles are hydrophobic (but can be treated to be hydrophilic). The interior fiber structures are hydrophilic.  Merino adds a level of complexity that my test has not addressed yet.  I am looking for people’s comments to suggest additional directions for the new testing device, and now I have the first one.  So, I will include some merino base layer fabrics in my next round.

I would say the question of fit depends on the type of base layer as well as the layering system.  When I am biking, I wear a loose bike jersey rather than a skin-tight one because that fit encourages air to penetrate the jersey fabric and circulate between the skin and the fabric.  This can enhance sweat evaporation.  In a multilayer system, significant air movement may not occur, limiting convection. A tight base layer can improve contact between moisture on the skin and the fabric of the base layer.  For a hydrophilic base layer that will improve initial wetting and subsequent wicking. For a hydrophobic layer, the tightness will ensure that the pressure drive I discuss in the article is readily available to send liquid moisture into and through the base layer.  So, loose or tight?  For multiple clothing layers, I generally tend towards a snug base layer.

My experiences with wool base layers are same as Steve’s, light as possible and loose fitting.  Wool is a greedy sponge, lighter ones hold onto less moisture.  Looser ones give some chance of bellowing air and drying out more quickly.  Thicker tight heavier ones to me are like wearing a wet shirt, they don’t spill off moisture fast enough to benefit from the tight fit.  If I sweat less, tight might be OK.

Wool plays a get out of jail free card, “warm when wet”.  I prefer warm and not wet.

Hi David:

What I saw for Lifa was that a lot of water gathered at skin side of the Lifa fabric. However, it could not travel through the Lifa at typical available pressures because the pores are too small.  There are two Lifa base layer skews. One has higher air permeability than the other.  The one I used here is the lower-air-permeability version. The higher air permeability version will move vapor better but will perform no better for moving liquid water.  In the higher air permeability version they double the area of the large pores structures. You can see a triangular pattern of pores in Figure 7.  These turn into diamond shapes in the high air perm version. Since the individual pores are the same dimensions, they will still resist water transmission at normal pressures, just like the version I tested.  A good layer to wear over Brynje in cold weather, when you want to keep air “trapped” in the Brynje, is the Gore shirt I tested. Unfortunately, Gore has closed Gore Bikewear so the Gore baselayer is slowly disappearing.  I bought several more. It works well in this role because its air permeability is less than Finetrack Basic.

One of the important lessons from the testing was the critical nature of the structure of hydrophobic base layers for effective moisture transfer.  If the pores aren’t large enough, water transfer won’t happen.  Finetrack Basic and Cool and Gore Baselayer recognize this in their fabric design and work very well.  I don’t know how many other hydrophobic base layers are available that can match their performance.  Lifa does not quite get it right.

Hi Stephen, my Lifa is the higher air permeability version but I agree it overloads with water easily.

Thanks for the lead on the Gore, I’m game to give it a shot.  Would that be the “Gore Wear M Base Layer”?  I see Gore M Base Windstopper and Thermos available but the regular is scarce.  To layer over a Brynje, should it be sized up? Fit looks body hugging.

I’d consider a Finetrack as a fall back.  Is the gsm in the table correct?   Basic/Cool thickness = 1.5 (.584/.381) but Cool/Basic gsm = 1.5 (75/48).  Maybe its the Basic version that is 75 gsm?  It’s hard to tell but the Basic also looks heavier from the picture.  I’d replace the Lifa with the warmer of the two

Thanks again.

I am 5’10”, 170 pounds.  I prefer the extra large.  This is the shirt. I wear the XL over Brynje or by itself.  It stretches.  On Finetrack. Use the Basic. I think the cool is just short sleeve. I have not worn Cool, I cut up the shirt for testing.  I have extensive experience with Basic.  I have enough experience with Warm to verify that it does not move sweat off the skin. Remarkably, Basic is the lightest fabric of the three. Finetrack is Japanese, not American sizing.  It is very stretchy.  I wear their largest size which is sort of equivalent to US large. You can see from the data table that Basic has  higher air permeability than all except Brynje, so it will provide the highest MVTR but also the best ventilation.

Interesting, that’s the thermo version.  I’m 6′ 158 so will look for the XL.  Here’s the regular M, much lighter duty.  Anecdotal comparison to inexpensive bases here.

For the Finetrack just to confirm, basic = “all season“?  XL as well?  Thanks again, Stephen.

I checked the box with a new shirt.  The Gore is called M BL. It is not the Thermo.  Competitive cyclist has the Black for $ 42 and the White for $49.  Also, I wear the XXL. Remember, these are bike gear. The XXL is a bit snug on me.  Since they are polypro, wash them in cold and hang to dry. For Finetrack,  I would use the Basic for three seasons. If you want one for warm weather, they have a short-sleeve version.

Interesting test. I must confess that a lot of the more scientific testing that I read about here goes somewhat over my head. But I appreciate the testing here, and find it interesting.

I’m a bit disappointed that 100% cotton, or perhaps 50/50 cotton-poly wasn’t tested as a control.

Hi J: There are lots of fabrics that can be tested, but I don’t think cotton is a commonly selected base layer fabric among BPL members. What were you hoping to learn about cotton in the context of this test?

Well, I guess a baseline comparison. I’m new to backpacking, but my go-to base layer for any kind if outdoor activity is usually always a cotton-poly shirt. Because that’s what I have.

I’d be curious to see how much better or worse it performs than others tested. (Likewise merino or Alpaca too…) I’d also be interested to see if there’s much difference between 100% cotton, and cotton-poly blend fabrics.

Cotton can take hours to dry.
In mid-summer, not a problem.
In cold rainy weather that behaviour can be fatal.
That is it in a nutshell.

Cheers

Cotton can take hours to dry.
In mid-summer, not a problem.
In cold rainy weather that behaviour can be fatal.
That is it in a nutshell.

Well, that is the oft repeated line, that “cotton kills.” But, quantitatively, just how bad, or how much worse is cotton, than Stephen’s test samples? Would a cotton-poly blend show improvement in water transmission – letting the water go…?

Would Cotton’s high capacity for absorbing & storing water cause an issue with Stephen’s test?

To be clear, I’m not upset with Stephen for not testing cotton, but I am curious how it would perform.

Just how bad would cotton compare? Bad enough for me to invest in a more expensive “performance” base layer?

JAshley73: Some of Stephen’s tests take a lot of time to perform, so he often picks fabrics that are of interest to him. It doesn’t mean that cotton is useless — it just isn’t as good as the selected fabrics in terms of low moisture absorption and easy release.

Cotton is terrific in a hot, dry, desert, where moisture evaporates quickly and cooling is desired. It can be adequate in hot and humid environments. Loose fit allows air movement underneath, which helps.

Cotton t-shirts might be the most common hiking shirt around the world. I have hiked a lot of summer miles in the same cotton dress shirts that I wore for work.

In my experience, poly-cotton isn’t usually as comfortable as plain cotton in the heat. It’s even less comfortable in hot and humid weather. But poly-cotton can be more rugged than lightweight pure cotton, so there’s a tradeoff there.

None of that is a direct answer to your question, of course, but qualitatively: most cotton fabrics absorb more moisture and release it more slowly than the state-of-the-art synthetic fabrics tested here.

Let’s keep sight of what this article is about: a fabric’s ability to remove liquid water from the skin and transfer it to the next layer. It is not about drying time, which we know is primarily a function of volume of trapped water, which in turn is primarily a function of fabric thickness. It is not about breathability. It is not about general comfort.  The test results show that hydrophobic fabrics tend to outperform hydrophilic fabrics. It is entirely possible that a fabric that is both hygroscopic and hydrophilic will retain more water than the hydrophilic fabrics I have already tested. I suspect that the receiving layer must exert even more capillary force on a cotton base layer to pull out moisture trapped in the fibers. I will try to find a knit cotton that is similar in thickness to the Delta fabric and include it in future testing.

Let’s keep sight of what this article is about: a fabric’s ability to remove liquid water from the skin and transfer it to the next layer. It is not about…

If I wasn’t clear in my previous posts about cotton, I would at least like to state for the record, that I was asking those questions about Cotton & Cotton-Poly within the context that you just stated. Thanks again. I found it quite enjoyable.

May I suggest that you test the following combo:

1. skin layer
2. Polartec Power Dry Silk Weight as base layer
3. Polartec Power Dry Silk Weight as receiving layer

I always begin with skin + thin loose fitting base layer (I prefer the term ‘moisture regulating layer’)

If cold enough I add a thin loose fitting base layer.

Woubeir:  are you suggesting substituting the silk weight for the paper towel receiving layer that has been used in the current article? Alternatively, are you suggesting adding an additional receiving layer which would then transfer to the paper towel receiving layer?

Competitive cyclist has the Black for $ 42

The Finetrack is NLA right now in Canada, and the Gore with shipping and exchange converts to $100 but is NLA anywhere else.  Considering it, thanks.

Commerce in Canada is nowhere near the selection as the US and cost of living here has gotten pretty crazy, worse than the US.   Getting harder and harder to justify trying new stuff out.

Good question. Mmmm.

Perhaps an additional layer so that the first Powerdry transfers to the 2nd Powerdry and the 2nd Powerdry tranfers to the paper towel.

And maybe, if you have thicker Powerdry, test this as you did here.

Just to see if my gutfeeling is right and that two thin layers over eachother are more efficient at moistureregulation than one thicker one while being (nearly) as efficient in providing warmth.

I have been playing with polypropylene recently, your article has really useful information, thanks.

I made some gaiters with polypropylene.  When I walked through wet brush and rain, the polypropylene stayed dry and no water went through to my pants and socks.  These would be very good gaiters.

Reading your article, I think I understand better what’s happening.  No pressure from the outside to the inside so no water will go through.

The only problem is that fabric is too low denier so it easily rips.  I made another with heavier polypropylene and will try it next.

I made some pants with polypropylene.  I think they would be good in rain just like my gaiters.  Which is consistent with your data.  Testing in future.

I soaked some polypropylene in water and was surprised that it gained 150% of it’s weight in water, I thought hygroscopic fabric didn’t absorb water.  Now I see what’s happening.

I have a polypropylene base layer shirt.  I’ve worn it a little.  Inspired by this article I need to use it some more.  This is what your article is more aimed at.

Another possible use for polypropylene is an outer layer when it’s raining.  I wonder if rain drops falling on it would mist through it.  Probably.  I’ll have to wear my polypropylene shirt in the rain.  Your testing doesn’t illuminate this.  I think.  In another article you tried to figure out if rain drops mist through a fabric from the pressure of rain drops, which questioned that as I remember.

On a WPB jacket of mine, in the rain, it wets out, then water accumulates on the inside of the WPB.  Then, that water wicks into the pockets and onto my shirt.  When I put a polypropylene layer between WPB and pocket, no water wicked through.  This is consistent with your data.

I made another jacket with polypropylene liner at pockets, shoulders, and hood.  I haven’t tested it yet.  Based on your results, I bet water will leak through at the shoulders and get my shirt wet. My pockets should stay dry.

I haven’t found a lot of polypropylene fabric.  There’s fabric intended for the under side of upholstery.  That is too light for gaiters but probably good enough for shirt.  Not sure about pants though.

There’s polypropylene intended for geotex or weed barrier that’s heavier.  I made gaiters from that.

Bill Bundy shared a link for a WPB jacket with polypropylene on the outside.  Maybe Japan?  But it wasn’t available?  I wonder how it performs in the rain.  It seems like it has a superior DWR without it poisoning us.  This article doesn’t help with this.

When I ironed the polypropylene to smooth out the wrinkles, it melted onto the iron.  Not to worry, just need to turn down temperature. It probably doesn’t matter that polypropylene has a lower melting temperature than polyester and nylon.

Woubeir: In fact, I had planned on looking at this in the next round. We might already have some insight. With the hydrophilic layers, as the receiving layer gains moisture, its ability to receive additional water from the underlying layer degrades. So, does having more or fewer fabric interfaces help or hinder the water handoff? Is there enough pressure in the system to replace all hydrophilic layers with hydrophobic layers?  Would this improve water transfer between layers, as we have seen in the present tests, and would this hold for multiple hydrophobic layers?

Hi Jerry: If you take the advertised polypro shell and place it in the washing maching machine, there will be some water trapped in the shell airspaces when you remove it.  At some point, forces are high enough to drive water into the airspaces of the hydrophobic fabric. The smaller the pore openings, the more pressure it will take for this to occur.  In principle, one should be able to design a polypropylene fabric to withstand torrential rain. What would that fabric look like in terms of fabric weight, fabric comfort and packability?  Maybe you will be able to tell us as you keep trying more fabrics.