From RCG HQ: Here’s Day 2 of Rebecca’s adventures at Gore-Tex Bloggers summit!
One of the most interesting parts of the Gore-Tex Blogger Summit was learning about the core science behind what makes a garment waterproof and breathable. This actually is important information for the outdoor consumer. It’s not unique to Gore-Tex and the science applies to all kinds of outerwear, manufacturers, and sports.
What exactly makes a jacket waterproof and breathable? What does breathable mean? Why do I get wet inside my Gore-Tex or eVent or other waterproof/breathable material jacket? In order to understand why a garment is or isn’t working for you, it helps to understand the science behind what is going on. Sometimes it’s not the jacket that fails – it’s science doing its best to make you uncomfortable.
“The laws of science be a harsh mistress.” – Bender, Futurama
Waterproof breathable membranes have one characteristic in common: they are porous in nature, and these pores are what keep water droplets out and allow water vapor to pass through. In an ePTFE membrane like Gore-Tex, the pores are approximately 20,000 times smaller than a droplet of liquid water, but 700 times bigger than a molecule of water vapor. Brad, our science guy for the day at Gore-Tex described it thusly: think of the membrane as a chain link fence, the water vapor as sand and the water droplets as beach balls. Throw a beach ball at the fence and it won’t fit through the holes. Throw a handful of sand at the fence and it will pass through.
What does waterproof mean?
It means exactly what you’d think – no liquid water can pass through the membrane. This has a lot to do with the properties of liquid water like surface tension and other sciencey mumbo-jumbo that I’ll steer clear of today. The bottom line is that liquid water in its smallest form is much larger than water vapor.
What does breathable mean?
This is a more complicated answer. Many people think that breathable means the ability for air to pass through, but this is not the case. Have you ever seen someone pick up a Gore-Tex jacket and try to blow through it? That’s permeability, not breathability. Permeability is a measurement more important to windproof fabrics. Breathability refers to the rate at which water vapor molecules pass through the membrane.
Just because water vapor can pass through the membrane doesn’t mean that it will do so in the most efficient way possible. As you sweat, the moisture is being vaporized by the heat that your body is putting out. This vapor will ideally ‘breathe’ through the pores in the membrane. However, this is where science steps in and does its best to mess with things.
The rate at which this movement happens is based on the how fast you are cranking out sweat and vaporizing it, the climate difference between your body and the outside, as well as the resistance of the layers between you and the outside. So, in reality, there are a lot of factors that go into how breathable you perceive a garment to be, and those factors are going to be different every time you use it.
In addition, if the membrane gets polluted with dirt and oils, it impedes its ability to let water vapor molecules pass through. Lastly, if the laminated textile (usually the outer fabric) ‘wets out’ it will prevent that vapor from passing through. The DWR (durable water repellent) that you find on most waterproof outerwear works as the first line of defense against the wetting out of the fabric, helping the water bead up and roll off. Maintaining the DWR coating will go a long way to making your waterproof/breathable outerwear more comfortable. I’ll focus on the care of DWR and waterproof/breathable garments in an upcoming post.
There is an ISO standard for measuring breathability, but the results are not commonly part of marketing or consumer materials. Unfortunately, tests of breathability can vary significantly due to the large number of variables described above and test method used. Since there is no consistent measurement between manufacturers, numbers on charts and labels can be misleading, especially when you are using them to compare garments.
What is the difference between all of the waterproof/breathable materials on the market?
My answer to this comes from W.L. Gore, so take this as you will. There are four core types of waterproof/breathable materials out there, three of which are based on polyurethane. The polyurethane membranes tend to perform at a lower standard in one or more of the following areas: waterproofness, durability, and breathability.
The fourth type is ePTFE. Gore-Tex, as described in the previous post, is made of this material. When W.L. Gore’s patent on this technology expired other competitors entered the market, the most well known of which is eVent. Gore freely admits that eVent has the same performance with regards to waterproofness and breathability, but claim that Gore-Tex is far superior in terms of durability and endurance.
Why? Well, although the ePTFE patent has expired, Gore still holds the patent on the idea of protective engineering. In other words, W.L. Gore has formulated a proprietary chemistry that can protect the membrane from sunscreens, oils, DEET, and other destructive materials. Remember, the accumulation of dirt and oils can seriously impact breathability, and Gore says their product is much better at keeping the membrane free of these contaminants.
I don’t know how long it takes a jacket to be contaminated to the point of reducing its effectiveness, but if you regularly junk up your waterproof garments with sweat, sunscreen, and DEET, it’s something to keep in mind.
Gore-Tex does not do proprietary branding for their customers. So any membrane that is specific to a manufacturer (like Mountain Hardwear Conduit, or Marmot Precip) is not made by Gore-Tex and is likely made of one or more of the three polyurethane types.
Why do I get wet in my Gore-Tex jacket?
Well, as described above there can be several reasons – climate conditions (temperature and humidity differences between your body and the outside), the resistance of your layering system as a whole, a dirt or oil polluted membrane, deterioration of the DWR, and many other factors. If you are cranking out the sweat faster than the system can keep up with it, it’s likely that you’ll get wet.
And you can’t forget to check the source of your jacket, too. One of the Gore associates said they will get returns of ‘Gore-Tex’ jackets where people complain that they don’t breathe, and it turns out they bought some kind of knockoff from eBay or other dubious source.
Sometimes, you will feel wet and clammy inside a waterproof breathable jacket even when you’re perfectly dry. This feeling is especially pronounced in outerwear that has deteriorated DWR. As the outer textile wets out in a cold rain it sits against your body. Your skin interprets the cold and pressure as moisture, when in reality you’re dry.
Coming Up: Science lesson over, thanks for bearing with me. Next, I’ll move on to the fun stuff: a tour through the Gore-Tex testing facilities (wind! cold! rain! Washing machines!), the seemingly backwards way to care for your Gore-Tex garments, and final impressions of the event.
When Rebecca isn’t busy getting her nerd on with trip reports and gear over at calipidder.com, she can be found somewhere in the backcountry of California, backpacking, hiking, climbing, photographing, o
r just soaking in the scenery. She communicates best at 140 characters at a time, so she looks forward to continuing the conversation at twitter.com/calipidder.
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