“Water resistant” and “waterproof” both refer to penetration of liquid water. Manufactured waterproof fabrics have been around for over a hundred years. They are either treated or are inherently resistant to water penetration and wetting. In Victorian times, Scottish inventor Charles Macintosh sandwiched rubber between cloth to make an impermeable fabric that was waterproof but not breathable. Raincoats were made from this material and became known as ‘macs’. However, the early designs smelled quite bad and melted in hot weather.
Gabardine was invented by Burberry in 1879 and for 40 years was the market leader for waterproof clothing. It consisted of tightly woven cotton. Subsequently, natural or synthetic fabrics have been laminated or coated with waterproofing substances such as rubber, polyvinyl chloride (PVC), polyurethane (PU), silicone elastomer, fluoropolymers, or wax. Coated fabrics tend to be very waterproof but lack breathability in comparison to membrane laminates.
These coated fabrics are less expensive and are improving as manufacturers finds ways to make the coatings thinner and more porous. Coated fabrics are great for emergency weather protection or for activities that don’t involve a high level of exertion.
During the twentieth century, several new water resistant fabrics were invented, including Gore-Tex®, a breathable membrane that contains billions of tiny pores which are too small to allow water droplets to pass through, but large enough to enable water vapour to evaporate. Its main rival in breathable fabric is eVent™, which uses a process called direct venting. Other developments include more flexibility in the sandwiched membranes, a feature included in Helly Hansen’s products. Some waterproof clothing does not use membranes, such as Nikwax Analogy and Pertex, both of which use inner liners that copy animal fur to pump water away from the body. Neoprene by DuPont™ is a synthetic rubber that can be used for sports protection and diving suits, as it is cheaper than breathable fabrics.
Not all water resistant fabric is used for clothing of course. Medium and heavyweight nylon, acrylic and polyester are suitable for making bags, groundsheets, awnings and waterproof coverings. Outdoor equipment manufacturer Karrimor was an innovator in the field in the 1960s, and developed nylon-elastomer fabrics that were robustly waterproof. Durable water repellent (DWR) coatings can be added to fabrics during the manufacturing stage, but at some stage their durability wears off and the material needs to be re-treated. A well-known example of DWR is Scotchgard™.
If a fabric or product is classified as “water repellent” as opposed to waterproof, this means it will repel water but is not impervious to it, or put in another way, there is a level of water pressure it can withstand before leaks start to appear. Just as with waterproof products, there are criteria that fabrics and textiles have to undergo in order to test their repellency and protection levels and thus be given an overall rating. The Bundesmann test is one way of measuring this by pouring a continuous shower of water over the surface of fabrics at a height to simulate rain. The amount of water that seeps through, in addition to the amount absorbed into the fabric is then measured and the fabric is given an efficiency rating based on performance.
Even the best waterproof raincoat can become soaked through if left for sufficiently long under water. However, a new invention from Switzerland uses revolutionary nanotechnology to produce a truly waterproof fabric by incorporating a layer of chemically hydrophobic (literally “water-hating”) silicone nano-filaments, produced in a one-step process, in which silicone gas condenses onto the fibres of the material. The coating can be added to many textiles, including wool, viscose and cotton, although polyester currently gives the best results. Scientists got the idea from natural examples of extreme water resistance, such as the surface of Lotus leaves.
Air is trapped between the silicone nano-filaments. This imitates the way some insects and spiders breathe underwater. Spraying a material with super-hydrophobic nano-particles which have tiny spaces between the particles that “reach up and grab” air particles creates an “umbrella of air” across the surface of a material that water cannot penetrate. From lightweight specialist clothing to suits which don’t get wet in the rain, nano-enhanced fabrics will become a more and more visible part of our lives in the future.