A Truly Amazing Material

When many of you head outdoors this season, whether for hunting or just to enjoy the crisp air, you’ll reap the benefits of technology and atmsopheric physics to help keep you dry. I still think one of the greatest innovations in outdoor equipment is fabric that is truly waterproof and windproof, yet allows moisture from your body to escape. This fabric goes by many names, but the most widely known is Gore-Tex.

The first time I encountered Gore-Tex was around 1980. I was a Boy Scout with Troop 103 in Atlanta, GA, and our assistant scoutmaster showed up for a campout wearing a light jacket that he said was completely waterproof and windproof. The rest of us had our standard ponchos made of nylon or rubberized fabric. Our ponchos kept rain out, but trapped so much body mositure that we still ended up damp. Of course, our ponchos cost about $5, while Paul’s fancy jacket cost almost $500. By the time we ended up back at the church after a soggy weekend in North Georgia, we all were true believers in this new “wonder fabric.”

Today, waterproof and windproof fabrics are a common component in not only lightweight rain jackets, but a wide range of outdoor clothing. But what makes these products work? The secret lies in the fact that water in the form of vapor is much smaller than a water droplet. In fact, your average raindrop is about two millimeters in diameter. This is obviously much larger than water in its vapor form.

A material that prevents two-millimeter raindrops from penetrating yet allows water vapor to escape must have extremely small pore spaces. This can’t be created by merely weaving cloth tightly. This needs a chemical production process.

According to the Gore-Tex Web site, Bob Gore created a synthetic material in 1969 that met these criteria. Its chemical designation is expanded polytetrafluoroethylene (abbreviated ePTFE). After some refinements, it was patented by Gore’s son, Robert, in 1976 and first marketed in 1978 under the trade name “Gore-Tex.”

The Gore-Tex membrane has more than nine billion microscopic pores that are about 20,000 times smaller than an average-sized raindrop, yet are about 700 times larger than a water vapor molecule. The result is that water in liquid form can’t penetrate the material, while water in vapor form easily passes through.

Of course, you probably aren’t thinking about the physics of your rain gear — just that it’s keeping you dry and protected. In the end, that’s the point of the product.

Have a great time in the field!