Ever wondered how some garments can be both waterproof and breathable? How they keep the rain out but allow your sweat to escape? Well read on and all will be revealed.
Probably the best known of all waterproof breathable fabrics is Gore-tex®. Although this is often used as a generic term for this type of fabrics, it is actually a brand name and registered trademark of W. L. Gore and Associates.
It traces its origin back to 1969 when two members of the Gore family discovered that by quickly stretching polytetrafluoroethylene (PTFE) fabric it formed a microporous structure that was about 70% air. Patents were quickly filed to protect this technology and various court cases and appeals ensued with other companies claiming prior usage of the technology.
Since the first invention of this technology, various competing brands have created their own version of waterproof breathable fabrics, such as Highlander's Ab-Tex, Grafters' Jon-Tex, Jack Pyke's Breathatex, to name just a few.
These breathable fabrics are all based on the same principle and they all consist of many tiny holes, or pores. Typically, a breathable fabric may have 9 billion such pores per square inch. Each of these pores measures 1/20,000 the size of a water droplet which means that it is impenetrable to liquid water. However, the smaller water vapour molecules, such as produced when sweating are small enough to pass right through. The fabric therefore acts as a waterproof membrane against rain on the outside while still allowing sweat vapour to escape, resulting in the wearer remaining completely dry underneath.
So that's what you can expect from any garment we describe as both "waterproof" and "breathable", such as our Waterproof Breathable Jackets or Waterproof Breathable Trousers.
The outside of these fabrics is usually coated in some form of water repellent treatment. This prevents a build up of water on the outer layer which would reduce the breathability. After prolonged use, the outer water repellency may have become reduced with use. This means that water can build up on the outer surface of the fabric, preventing sweat vapour from escaping which in turn can lead to damp patches underneath. This often leads the wearer to believe the garment is no longer waterproof. However, a re-application of a water repellent treatment should resolve the issue.
To further aid waterproofing, you will often find seams of garments are taped over on the inside, as these areas represent weak points where water may be more likely to enter.
So the next time you get caught in a downpour of rain, remember it's all those billions of tiny holes keeping you dry!
June 2019
