The debate continues in the outdoor industry over what is the best waterproof breathable fabric. This has led to much confusion at the consumer level as to how to choose between waterproof breathable fabrics and what actually is the difference. T.D. Wood gives a great, detailed explanation over on the REI Expert Advice blog about what exactly is waterproof breathable fabric and how it works. I will try and sum up the highlights here for you.
Waterproof breathable fabric is engineered to handle two tasks simultaneously: repel precipitation and release perspiration vapor. To make fabric waterproof breathable requires work on both the inside and the outside of the garment.
Lets talk about the inside first as this is where much of the confusion comes from. The inside of the garment uses either a laminate or coating technology. Laminates (which include Gore-Tex and eVent) are formed when a waterproof breathable membrane is bonded to the underside of a fabric. Coatings (such as The North Face's Hyvent) are liquid waterproof breathable substances that are spread thinly across the interior of the garment. Coatings are usually less sophisticated, less expensive and provide for lighter weight garments than laminates.
Laminate membranes can be made from three different materials (excuse the acronyms here): ePTFE (basically Teflon), Polyurethane (PU) films or Polyester films. Gore-Tex uses a combination of ePTFE and PU, while eVent simply uses ePTFE (with some secret sauce). This difference in materials used is where much of the debate over which fabric is more breathable stems from. The argument is that since Gore-Tex uses a PU film over their ePTFE material, it takes more work for the perspiration vapors to get through the fabric. Throw in Marmot's new PU film based MemBrain Strata , which is giving Gore-Tex and eVent a run for their money on breathability performance, and now you have a real mess.
In terms of the outside, all waterproof and even water resistant softshell garments are treated with what is called a DWR (durable water repellent) finish. DWRs do not inhibit fabric breathability and are there simply to protect the face fabric from becoming saturated with precipitation. Xeromax Sciences, a start-up company we have posted about previously, is a new entrant on the DWR scene.
So which waterproof breathable fabric is the best? The answer is it depends- which is probably why you see so many people swearing by one technology or the other. One of the problems is that there is no accepted standard for testing fabric breathability and it is almost impossible for any one test to mimic the changing conditions you experience while outdoors wearing the garment.
Regardless of whether you are wearing a garment with Gore-Tex, eVent or MemBrain Strata, moisture will transfer out of your garment faster if the contrast between inside your jacket and the air outside is high. So as you work up a sweat in cool conditions, the less difference you will probably be able to find between the high end waterproof breathable fabrics. It basically comes down to individual perception of breathability.
So which fabric do you prefer?