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Breathable waterproof fabrics have evolved greatly since W. L. Gore first created Gore-Tex back in 1969. The first fabrics were expensive, limited in variations, and did not have the long lasting-qualities of some of today’s fabrics. This blog is a basic intro on breathable waterproof fabrics and how they work. I have attempted to keep it as simple as possible in the interest of brevity.
We now have many different brands of waterproof breathable fabrics that vary widely in weight, uses, breathability, waterproofness and quality. At the core of every breathable waterproof fabric is a very thin layer of PTFE. This is an acronym for Polytetrafluoroethylene. Most likely neither you, nor I, can pronounce that word, luckily it is more commonly known as Teflon. Rather than being adhered to a kitchen pan, it has been stretched quickly into a very thin porous layer. These pores are microscopic, and the physical difference between liquid and vaporized H2O molecules allows for a membrane that can do what at one time would have been considered impossible. The pores are really small, about 1/20,000 the size of a drop of water. The surface tension of water does not allow for the liquid to penetrate the fabric. On the other hand, vaporized water molecules are smaller and lack the surface tension of liquid water, allowing them to pass through the fabric unimpeded.
The PTFE layer on its own is too delicate to work on its own, so it has to be part of a laminate. Protective layers are applied on both sides for durability and added features. You have may have heard of 2, 2.5, 3, 4 and now 5-layer fabrics. The exterior can be nylon or polyester which is then treated with a DWR or Durable Water Repellent. This does not actually keep the fabric waterproof; rather it allows it to remain breathable in wet conditions. With time this will wear off and can lead to the sensation that your fabric is leaking, however it is more likely that it has lost its DWR, and in turn, breathability. As a result, your body perspiration is condensing inside the fabric rather escaping through the material.
The interior has another protective layer of lighter weight creating a 3-layer fabric. There is often another softer face layer that makes the fabric more comfortable for skin contact. This is known as a 4-layer fabric. There are also 5-layer fabrics; these have two layers of PTFE. These are typically very waterproof but have very poor breathability.
Regarding waterproofness and breathability, for different applications there are unique needs depending on the environment. A mountain climber or skier in a low humidity environment who will be sweating for hours or days will have needs different from a duck hunter chest deep in a marsh. Waterproof testing varies greatly and there is not one single standard, plus, tests in a lab do not always perform in the same way when exposed Mother Nature. So, to keep from getting too deep into the weeds, a typical grade would look like this 15,000/6,000. The first number is how waterproof the fabric is. The scale begins around 5,000 and goes to around 30,000. Some lightweight rain shells are around 10,000. Fully waterproof fabric is in the 20,000 range. The second number is breathability. Breathability runs the same range, the higher the number the more breathable. Of course, as you go higher in waterproofness, you typically get less breathability.
Breathable chest waders are now very popular due to their versatility, light weight and comfort. When choosing a breathable wader there are a lot of factors to consider beyond just the fabric. Putting those other factors aside, a 4 layer is going to be the best all-around option for durability, comfort and longevity. A grade of 20,000/5,000 is a good balance for breathability and waterproofness as keeping water out is most important when submerged. Maintenance is pretty simple with most of today’s fabrics simply requiring a rinse of fresh water at the end of the day. After extended use, a treatment with a DWR can help to extend the effectiveness of the fabric. A good option is Nikwax spray-on DWR
This is just a basic intro on waterproof breathable fabrics. If you start to dig deeper into the subject it can be a little bit overwhelming. If you follow these basic guidelines and buy from a company that you trust, you should stay dry and comfortable throughout a range of situations.