By the Numbers: The New Breathability Gap in WPB Jackets and What the Breathability Tests Get Wrong

In 2021, I wrote an article called By the Numbers: The Search for a High-MVTR Waterproof-Breathable Shell Jacket. I tested 18 jackets and found only three that I considered highly breathable. Since then, I have continued testing jackets while searching for better-performing options, and a lot has changed.

Most importantly, PFAS chemicals have been removed from much of the U.S. waterproof-breathable market. Those chemicals helped make microporous membranes highly hydrophobic and helped face fabrics repel water. Their removal has greatly reduced the role of ePTFE and increased reliance on monolithic hydrophilic polyurethane (MHPU) membranes.

This change matters because MHPU membranes usually do not transport moisture vapor as well as microporous membranes under normal use. Based on Gibson’s data, MHPU membranes deliver roughly 25-50% of the MVTR of eVent, a microporous membrane. However, common tests that measure MHPU breathability can exaggerate performance by using conditions that aren’t typical of regular use.

In this article, I tested 21 current jackets and fabrics and compared them with results from my 2021 study. We will look at how membrane technology has changed, why different membrane types behave so differently, and why the MVTR number printed on a hangtag may tell you surprisingly little about how a jacket will perform on the trail.

In short, you will learn how WPB fabrics work, how to interpret breathability claims, and how to make more informed buying choices. We’ll end with a brief look at market developments likely to shape WPB fabrics over the next few years.

Gore-Tex, the 800-pound WPB Gorilla—A quick look at what has changed

During the past few years, Gore-Tex eliminated PFAS chemicals in its products and introduced a new membrane called ePE.

Since Gore-Tex’s introduction, Gore shifted from fully microporous ePTFE to a bicomponent design that pairs ePTFE with a thin monolithic PU coating. The PU coating helped prevent clogged pores. It also reduced breathability. Eventually, Gore introduced the Pro membrane, which eliminated the PU coating for their premium WPB fabrics and improved breathability.

Today’s ePE construction may seem similar to former Gore membranes, but it is very different. Now, the MHPU layer provides vapor transport and water resistance, while the underlying expanded polyethylene it attaches to provides a load-bearing scaffold that contributes limited breathability and water resistance. The membrane construction is found in US Patent 12,043,713 B2.

How do these changes play out in MVTR performance? Table 1 shows reductions from prior Gore standard and Pro membranes.

Table 1: MVTR Comparison of ePE and ePE Pro with former like models

Why the large reduction in Pro MVTR performance? A review of web publications quickly revealed changes from the old Pro to the new ePE Pro. Facewest states that Gore-Tex Pro uses the same ePE membrane as standard Gore-Tex, with a more durable outer face fabric as the distinguishing feature, and Wild similarly reports that Gore-Tex Pro ePE products share the same PFAS-free ePE membrane as standard ePE, differing only in face fabrics and backers optimized for durability. So, current ePE membranes share the same structure across the entire product line; any remaining performance differences between tiers likely come from face and liner fabric choices, not the membrane itself.

Some perspective helps. In my 2021 testing, Gore Shakedry was one of the best-performing membranes I measured, at 3,360 g/m²/24h. But most other Gore-Tex products were not at the top of the market. Other top performers in 2021 were the OR Motive at 3,360 and the Marmot PreCip Eco at 3,120. So even before ePE, Gore-Tex was not consistently the breathability leader. As we will see, the new ePE products fall even farther behind today’s best microporous membranes.

Section 1: The Measured Data — 2017 to 2026

Table 3 lists WPB jackets and fabric samples measured on my Permeation Kettles for the 2026 and 2021 studies. The jackets tested for model years 2025/2026 are shown in boldface. Each tested garment or fabric is grouped by brand and model so repeated or related models sit near each other—Arcteryx Beta LT 2021 next to Arcteryx Beta SL 2026, Marmot PreCip Eco 2021 next to Marmot PreCip Eco 2026, and so on. Testing spans model years 2017 through 2026. A more focused comparison (Table 4), pairing nine of these jackets directly against the model they replaced, follows the full table below.

Membrane Trade Names: Many manufacturers use a generic name for their membranes. That generic name may be applied to both hydrophilic monolithic membranes and microporous membranes. In many cases, I don’t know more about them than their name, so measured MVTR is often my best clue as to type. Microporous membranes will tend to have higher MVTR performance. Hydrophilic monolithic membranes will tend to have lower MVTR performance. There is likely to be some overlap in the middle: possibly 1700 g/m²/24 hours to 2200 g/m²/24 hours.

Before getting to the entire list of jackets, here are the best performers this year:

Table 2: Best MVTR Performers Tested this Year

The best performers are all microporous membranes. Later we will learn why. The Outdoor Vitals Tushar is listed twice because it contains different front and rear fabrics. Outdoor Vitals claims that Laminate 2 is MHPU. In Section 3, I will show why I believe it is microporous. Their Toray Torain fabrics provide excellent MVTR performance. After I wore the jacket for one hour, I observed changes to the interior coating, possibly from contact with sunscreen. Outdoor Vitals subsequently stated that, according to Toray, the coating was discolored rather than damaged and that washing may reduce or eliminate the discoloration. These claims have not been independently verified. Now, on to Table 3.

Table 3: 2021 and 2026 WPB Jacket MVTR Test Results

All MVTR values were measured on the Permeation Kettle at a constant 0.300 psi (2.069 kPa) vapor pressure differential. Four samples marked “fabric” were tested as fabric rather than as complete garments; all other values are whole-jacket measurements.