Be Prepared to Be Shocked About Gore-tex
Be prepared to be shocked about how Gore-tex and other products work. It is a cautionary tale of manufacturer’s claims and the actual scientific real world performance with advertising that is less than accurate and possibly misrepresenting.
BynstromI know you have tons of knowledge, so totally respectful.
I too had this take on it for years. And I am a tech head of sorts as well.
I think the science paper will surprise you, it certainly did me!
I found the link
Waterproof Breathable Fabric Technologies: A Comprehensive Primer and State of the Market Technology Review by Alan Dixon, Ph.D. (MIT)
http://www.backpackinglight.com/cgi-bin/backpackinglight/00316.html
IMO what remains to be seen is how eVent holds up in marine environment, and whether in conditions we face it is superior to XCR and the specific formulation that Kokatat uses.
Good reading and best regards
Tideplay
Small part of article follows
How Gore-Tex Really Works (The Answer May Surprise You)
First we’ll cover Gore-Tex, the (aging) granddaddy of all waterproof breathable membranes. More than 25 years ago, W. L. Gore created a thin membrane of expanded PTFE (a.k.a., “Teflon”; with a physical structure akin to a filamentous web). This membrane was waterproof but let water in gas form pass through (a micro-porous membrane). Presto, a waterproof breathable membrane!
How does it work? The common myth is that the spaces between the PTFE filaments are large enough to let water in a gas form pass through, but small enough to prevent water in liquid form to pass through. This is not exactly true. In fact, there is plenty of room for liquid water to pass through the spaces between the PTFE filaments!
More correctly, the surface of the PTFE membrane is at a high surface energy level (in lay terms, this means that it is extremely water repellent, or hydrophobic). Water in liquid form is repelled with such force (resistance to capillary wicking) that it takes a great deal of pressure to push it through the PTFE membrane. Water at a pressure resulting from a heavy rain doesn’t begin to reach this level. Conversely, if something were to take the membrane’s surface to a lower energy level, the water repellency would be lost and water would pass through the spaces between its filaments via capillary wicking. This is “first generation” Gore-Tex fabric and exclusively relies on the hydrophobicity of the microporous membrane for its water resistance.
When first generation Gore-Tex appeared in rainwear, it worked great - for awhile. However, customers began returning garments that had begun to leak. Here’s what happened: body oils, detergents, dirt and other common chemicals contaminated the PTFE membrane from inside. The membrane’s surface was initially effective enough to repel water, but it couldn’t repel these contaminants. Contaminant adsorption to the PTFE surface decreased its surface energy, creating pore channels with poor water repellency that wicked moisture through the membrane’s structure - not exactly the functionality you want in a waterproof garment. The result: the garment leaked. (It is worth noting that a fully expanded PTFE membrane can have an air porosity as high as 80% - so there is plenty space between the filaments for water to wick.) Thus, both surface energy as well as pore size are important factors affecting the waterproofness of a membrane. Gore learned the hard way the consequences of failing to recognize the long-term consequences of contaminant fouling of expanded PTFE.
Gore engineers tried to design a technology to keep the membrane free of contamination. The result: cover the PTFE surface with another membrane to protect it from contamination. The choice for this second membrane was polyurethane (PU). But how was water vapor to get through the fabric, since the pores of PU in its natural state are not large enough to be permeable to water - in either liquid or gas form?
The trick was to chemically modify the PU to be water absorbent (hydrophilic). Water in gas or liquid form is adsorbed by the PU membrane when it comes in contact with the membrane’s surface. Once adsorbed to the membrane surface, individual water molecules are then transported via solid state diffusion to the outer surface of the PU membrane. Diffusion is a chemical process where a substance at high concentration is transported to a region of lower concentration. In the case of solid state diffusion of water through a PU membrane, individual water molecules in their liquid form (H2O) creep their way through the PU matrix, driven by the concentration gradient formed by a high concentration of water on the wet inner surface to a low concentration of water on the dry outer surface. Once the water molecule reaches the outer surface of the PU membrane, it can then evaporate (become a gas phase molecule) and transport via gas phase diffusion through the PTFE membrane. It is important to note that the PU membrane is solid (monolithic). There are no spaces for a gas or water to pass though it. Water in either gas or liquid form is transported on a molecular level through the solid PU membrane (solid state diffusion). We refer to this type of PU membrane as a hydrophilic monolithic membrane.
So far so good. Gore had prevented contamination and they engineered breathability in the form of water molecule transport by solid state diffusion thought the PU membrane. Now the real problems start: the solid PU membrane moved water at a rate significantly less than the original PTFE membrane it covered! Thus, Gore made this membrane as thin as possible (see durability issues in the next paragraph), achieving a level of performance that was sufficient to bring the technology to market and they marketed Gore-Tex with its new PU membrane protection. This use of a hydrophobic micro-porous PTFE membrane covered by a PU hydrophilic monolithic membrane is often termed “second generation” Gore-Tex. Gore has made improvements in both weight and breathability relative to first generation Gore-Tex with the development of fabrics such as PacLite III and XCR, but they still employ the basic PU-PTFE membrane technology used in second generation Gore-Tex.
One final issue: PU-PTFE Gore-Tex membrane was delicate, resulting from an ultrathin PU layer, and had to be protected. Wear abuse causes pinholes and cracks to develop in the membrane and create leakage channels. Protection for the Gore-Tex membrane was accomplished by either adding a free hanging nylon liner on the inside of the garment or (more commonly used nowadays), by laminating a protective layer of polyester tricot to the inner surface of the garment. The latter type of construction is used in what is commonly known as “3-layer” fabric. Typically (unless laminated to an extremely light face fabric), three-layer fabrics are bulky, heavy and compress poorly. Gore’s 2.5-layer PacLite III mitigates some of these problems by substituting a textured surface pattern on the inner face of the WP/B membrane in lieu of the heavier and bulkier tricot inner liner.
eVent How does it work
What if you could use the original expanded PTFE membrane and not have to cover it with a PU membrane? You’d have a waterproof breathable membrane that would move moisture approximately 30% to 200% faster than Gore-Tex XCR*. BHA Technologies has developed such a membrane, branded as eVENT. Sounds like first generation Gore-Tex, doesn’t it? Here’s the difference: BHA engineered the PTFE membrane to be oleophobic, and thus, highly resistant to contaminant fouling. The eVENT PTFE membrane repels most of the common oily contaminates that originally plagued the first generation Gore-Tex membrane. Thus, eVENT does not need a breathability-inhibiting PU membrane to protect it from contaminants.
With unimpeded spaces between fibers (a micro-porous membrane), eVENT’s moisture transmission behavior is more like an uncoated woven or knit fabric. From Figure 1, you can see how closely eVENT matches the performance of Schoeller’s Dryskin Extreme, a stretch woven fabric that has no WP/B membrane (note that the air permeability effects of a fabric on moisture transport are eliminated in this test; if air permeability is considered, much higher moisture transmission rates would be measured for Schoeller Dryskin Extreme).
eVENT’s membrane structure is important in two ways. First, molecules in their gaseous state (including perspiration vapor) can pass through the pore channels between the membrane’s fibers, a process that is capable of moving significantly higher fluxes of moisture than what is possible for by a solid layer of PU (as in Gore-Tex). Second, and more important, eVENT passes moisture equally well at both low and high humidity levels, evidenced by the independence of eVENT’s moisture transmission rate on the humidity level (see Figure 1). At a 70% mean humidity level, eVENT transports moisture about 30% faster than XCR and about 70% faster than standard Gore-Tex and the best PU membranes. But at a 30% mean humidity level, eVENT transports moisture about 200% faster than XCR and about 250% faster than standard Gore-Tex and the best PU membranes.
