From the PCT to MVTR

In 1974 a friend and I celebrated our high school graduation by hiking the Pacific Crest Trail from Mexico to Canada. Of course we weren't suspect of our gear at the time, but looking back I can’t believe how much of it was really ill-suited for the job. Near the top of that list was rainwear. For those of us who remember the pre Gore-Tex™ era, it’s hard to believe that urethane-coated nylon was really all we had to keep dry back then. (Well, there was Foamback, but that’s a whole other story).

Because it was the lightest raincoat I could find, I took a Trailwise Coated Anorak (if you remember Trailwise, you’re really dating yourself). I often wondered as I plodded along in the rain if I would be drier if I just took it off. But since this was also before Capilene® and even polypropylene, I was wearing the uniform of the 70's hiker: a cotton t-shirt and jeans. Getting those things wet was something to be avoided at all costs.

Just 3 years later in 1977, my PCT partner Tony and his brother Jon set off on the Continental Divide Trail. They were the proud owners of perhaps the first incarnation of the Gore-Tex™ shell, The Early Winters Gore-Tex™ jacket. After they finished I asked what they thought of this new fangled Gore-Tex™stuff.

[Top: High along the PCT in the North Cascades. Bottom: Not-So-Old-School getting ready for the hike of a lifetime. Photos, Old School]

While light-years ahead of my coated anorak, Tony and Jon agreed that this early Gore-Tex™(now known as First Generation Gore-Tex™) was the first step toward something that would eventually change the way people dressed for the outdoors. Among the early problems they experienced were issues with the construction and the fabric itself. This was in the days before factory seam-sealing, which meant whenever you bought a new rain jacket you spent an evening or two with a tube of seam sealant carefully sealing each and every seam. Jon and Tony dutifully sealed every seam but to no avail; both said that water poured through the seams like they were sieves.

The other problem was a little more mysterious, and had to do with the fabric. Gore-Tex™, both then and now, is made from expanded PTFE (Polytetrafluoroethylene, think stretched-out Teflon™) that is glued onto the jacket’s outer fabric, usually a more durable material such as nylon or polyester.

In the lab, first generation Gore-Tex™ was wonderful stuff; super breathable, totally waterproof. In short, it was a backpacker’s dream come true. Only in the field did things began to go awry. It turns out there was one thing nobody thought of: when body oils and sweat came into contact with the PTFE laminate the PTFE became altered in such a way as to be rendered, well, not waterproof. WL Gore went back to work and soon had a solution; a very thin layer of polyurethane was laminated onto the PTFE layer, creating a barrier from oil and sweat. It worked. While the addition of the polyurethane layer did reduce the breathability of the fabric, it accomplished the more important goal of preventing the debilitating contamination of sweat and body oils. Factory seam-sealing took care of the seam leakage and by the early 80’s, Gore-Tex™ was synonymous with waterproof-breathable fabric.

Thirty years later, Gore-Tex™ is no longer the only game in town. It has lots of competitors, from eVent™ to Hyvent™ to PreCip™, to our own H2NO™. No longer is being simply "breathable" good enough. With all these new fabrics in existence, fabric designers needed a way to compare and quantify just how breathable these fabrics really were. The measurement they developed is called the Moisture Vapor Transfer Rate (MVTR). While MVTR is one of those terms some tech weenies love to throw at you, most of us have no idea what it means. But if you've ever asked how breathable a jacket is, what you've really asked is “what is the MVTR of the fabric in this jacket?" This is an important measurement, and as it turns out, not an easy one to make.

MVTR is generally given as Xg/m2/24 hours, where X is the amount of water in grams passing through the barrier per square meter of fabric in 24 hours. And while it sounds pretty straight forward, if you have ever called us and asked for the MVTR (or, more likely the breathability) of any of our fabrics you were probably told that we don’t give those numbers out. Someone might have even said that those numbers were proprietary. While it’s true that we don’t give the numbers out, it’s not so much that they’re proprietary. It’s a whole lot more complex than that. Randy is the man in charge of Quality Assurance for Patagonia so I went to him for a more detailed explanation of why we keep these numbers so close to our chest.

It turns out that obtaining an accurate MVTR is incredibly difficult. When Patagonia first decided to test the breathability of our fabrics, we chose six different fabric labs around the world and sent off a piece of fabric cut from the same bolt to each lab. When the results came back it was both disappointing and enlightening. All six results were substantially different, so much so that you’d have sworn they tested different fabrics. The Quality Team then went one step further; they took the exact same piece of fabric and sent it back to the exact same lab to be retested. Wouldn’t you know it, the second laboratory tests did not reliably match the first set. Obviously, if independent laboratories couldn't provide similar results from the exact same fabric, comparisons between different fabrics (and brands) were impossible. This discrepancy is the reason we don't publish hard and fast numbers; any comparison with other fabrics would be meaningless. Anyone picking a product based on one published number is putting a lot of faith in a marketing team and an unknown lab.

Nowadays, a budding outdoor clothing company can barely hang their shingle before the door is beaten down by fabric reps, plying their wares. But back in the early days of Patagonia when outdoor fabrics were hard to come by, off-the-shelf fabrics were often the only thing available (the fabric for the original Patagonia Pile Jacket was being sold as material for toilet seat covers). So, we’ve always tested fabrics ourselves in our own Fabric Lab.

Disappointed by the MVTR results of commercial testing, Randy and his team came up with a solution: they made their own machine. Randy explained to me how it works but to tell the truth all I remember is that it involves fans, humidity, thermometers and exacting measurements. This machine gives results that are accurate, and more importantly, solves the elusive repeatability problem that plagued the other labs. Our team was not alone in being impressed with the results; a few of the labs we originally used have even sent engineers to our Fabric Lab in Ventura to see how they did it. 

Today, our Fabric Lab team uses this machine to test not only our fabrics but those of our competitors as well. Every fabric we use (or don’t use) has gone through this and many other rigorous tests. Again, while we believe our MTVR test to be accurate, comparing our results to those of other labs will most certainly be meaningless.

It is important to note that Patagonia does not just rely on lab tests when picking fabrics. We also have a whole team of product testers, both formal (the pros, 1, 2, 3) and informal (the rest of us, 1, 2, 3) who give new fabrics and designs the real test. How waterproof and breathable are these fabrics really?

We believe that this combination of lab and real world tests gives us the best performance in the industry, but the more important test is you. What do you think? Let us know. We can’t pay you to try our stuff but we love getting feedback and we promise to listen. Your comments play a major role in our new and redesigned products.(1)

[Top, cruising the North Cascades. Photo: Old School. Bottom, MVTR test machine. Photo: RJ Hosking. Celebrating the end of a long walk . . . in jeans.  Photo: Old School]

Comments

[twosevens]

Far out, man!

[B Love]

Great article Ken! I would like to know where humidity factors into the equation with waterproof/ breathable fabrics. As any self respecting Southeasterner will tell you, there's no waterproof jacket on the market that is breathable when the outside humidity is at a high percentage (which is the case throughout the Southeast during most of its backpacking season). Also, at what humidity level is MVTR tested... I would think it would need to be at a constant for accurate results... would this constant be 0% humidity?

[Kevin]

Ken did you ever think that those clothes would be the pinnacle of hipster fashion now you would so fit in San Francisco or Portland these days

[Randy Harward - Patagonia Quality/Lab Dept.]

An MVTR test uses a humidity difference to create a vapor pressure between the inside and outside of a fabric. We run ours so the inside of the fabric is at or as close as possible to 100% RH and the outside is maintained at a very even (computer controlled) 50% RH. These settings may not sound like they are "real world" but the test must be run with no temperature gradient between the inside and outside, and it is run at our standard controlled lab temperature of 73F. What these operating conditions nicely create however is a small vapor pressure similar to what exists on a very warm and humid day. It's a worse case scenario so we make sure that materials will perform to our standards even when it's hot and humid. Of course the cooler and dryer it is outside the better the breathability performance.

[Old School]

Thanks for that answer Randy, I was wondering the same thing.

[fishtoes2000]

I have found that the term breathability is mostly hype. The materials may work in these limited tests, but I have yet to find to work in real life around the Great Lakes region.

As part of Patagonia's hugely commendable push for transparency, I'd like to see tests across a spectrum of realistic conditions. When the fabric doesn't breathe, say so. When the material doesn't shed moisture during active sports, say so. Tell us when they don't work in winter conditions. Don't set our expectations high then fail to deliver.

From my perspective, the biggest trap many manufacturers have fallen into is they believe material breathability works better than it does. As a result, they fail to design their garments with adequate venting -- which actually breathes well all the time under all conditions.

Fishtoes2000,
Thanks for your comments, as B Love and Randy alluded to above, the laws of physics pretty much prevent any waterproof/breathable fabric from breathing when the temperature and humidity are similar on both sides of the fabric. There needs to be some sort of pressure differential to push the water vapor through the membrane, and in some climates there just isn't. Out here in the drier west I have found these fabrics to work remarkably well.

I agree that the industry as a whole has hyped these fabrics beyond what is possible, if you're working hard in the pouring rain and you're sweating profusely, nothing can keep you dry and that's a message I think the industry has been reluctant to acknowledge. But that said Patagonia has, ever since we started using these fabrics, always addressed their limits. YC was famously skeptical of waterproof/breathable fabrics in the early years so even before we introduced our first w/b fabric (H2NO Storm) in 1988 we had H2No Plus, introduced in 1984 which was really an early soft shell and marketed as a more breathable but less waterproof alternative to all waterproof shells on the market.

Today, Patagonia and our competitors as well all sell a full complement of soft shells, intended to fill the gap between getting soaked from rain and getting soaked from your own sweat. Picking the garment that works best for you requires a bit of trial and error and also some 'reading between the lines' of catalog copy since most companies are loath to admit anything that sounds like a short-coming.

For us, our most breathable shells are going to be found in our "Velocity" line, all garments are geared toward highly aerobic sports. If you're looking for a more all purpose shell, still highly breathable but with more room for insulation check out some of our alpine soft shells. I find both the Houdini and the Ready Mix both super useful in conditions where a hard shell would be too much.

In the end though, if you're outside working hard in the pouring rain, you're going to get a bit wet, no matter what you're wearing but it really is (as YC has been known to say) just water.
-old school

[fishtoes2000]

That's for the response. I would disagree that Patagonia has always been up front. When I've purchased jackets marketed as "breathable" I don't recall nearby disclaimer in the catalog or one the web site explaining that they only work under some conditions. I realize that Patagonia's competitors don't either.

Yes, I totally agree about the Houdini line being a great light alternative. That is an awesome product. The Nine Trails jacket is really a great product as well.

[Nato]

One curious thing about MVTR is that it yields the result that Gore-tex is "more breathable" than basic 200 weight fleece. The problem is that the test is affected by the thickness or insulation value of the fabric. Fleece is clearly more breathable but that's not what the test results say. So something is amiss.

The DMPC test is way more accurate for truly perceptible, real-world "breathability". For info on DMPC check out: http://www.ssc.army.mil/about/pao/pubs/warrior/97/aug/breathe.htm

[AM]

Fascinating stuff...It leaves me wondering, What are the differences between the DMPC machine and the one Randy and his team at Patagonia have developed?