GORE-TEX®

Last updated: December 1, 2009.

The great American poet Henry Wadsworth Longfellow (1807–1882) once said: "The best thing one can do when it's raining is to let it rain." If he'd lived a few decades longer, he might have come to a different conclusion. Generally, the best thing you can do nowadays when it's raining is to reach for the GORE-TEX to keep yourself dry.

GORE-TEX is an amazing breathable, waterproof textile found in high-performance clothes such as walking/hiking boots and mountain coats. Unlike ordinary synthetic textiles like nylon, GORE-TEX stops rain from getting in but lets perspiration out. So it keeps you dry on the outside and dry on the inside at the same time. Sounds remarkable, doesn it? But how exactly does it work?

Photo: My fantastic GORE-TEX walking boots. They're leather on the outside, but the lining is made of completely waterproof GORE-TEX. You can jump in puddles all day long in a pair of these and your feet won't get wet.

Really Cooking

Photo: Look inside the boots and you can clearly see the GORE-TEX lining. The GORE-TEX fabric is inside the leather "uppers". The leather keeps out some of the water; the GORE-TEX keeps out the rest.

Suppose you're in the kitchen on a cold winter's day and you've got pans boiling away on the stove. Pretty soon, the windows are steaming up with condensation and the whole place feels like a sauna. But there's a storm outside and the rain is practically blowing sideways. What do you do? Well if you have sash windows (ones that open vertically at the top and bottom), you could open the top window just a fraction. Then the steam will drift out without the rain getting in. You'll let water out without letting rain in. Roughly speaking, GORE-TEX works the same way. It allows perspiration to escape one way through your clothes without letting rain come in the other way.

Is that some kind of magic trick? How can water flow through your clothes in only one direction? GORE-TEX isn't one simple material: it's actually a sandwich of three layers. There are two layers of nylon making up the "bread" and then a layer of microporous Teflon® (a brand name for polytetrafluoroethylene or PTFE) in between. You might know Teflon as the slippery coating on non-stick cookware. (Many people think it's a hi-tech remnant from the Apollo moon-landing program, but it was accidentally invented back in 1938 by a DuPont chemist called Roy Plunkett (1910–1994), who was trying to make a better refrigerator.) Teflon's slippery nature makes it great for waterproofing things. Some buildings, including the infamous Millennium Dome in London, are even made with gigantic Teflon roofs. Now no-one's interested in boiling an egg on top of a tent in east London; the Teflon's there to keep out the rain.

Photo: Ordinary detergents will clean your clothes but leave them considerably less waterproof. Always follow the manufacturer's cleaning instructions and be sure to use proper cleaning and waterproofing products designed specially for GORE-TEX and similar materials, such as Nikwax.

Liquid and gas

Now the Teflon in GORE-TEX isn't quite waterproof because it has tiny holes (or pores) in it. That's why it's called microporous Teflon. The pores are less than one micrometer (one millionth of a meter) in diameter—less than one fiftieth the size of a human hair. And this helps to explain why water in one form can't pass through but water in a different form can.

When you sweat, your body produces steam, which is water in the form of a gas. As you probably know, the molecules in a gas are not really joined together. They can whizz freely all over the place, which is why a gas fills whatever it's contained in. Now a water molecule is about 700 times smaller than the pores in microporous GORE-TEX, so when you sweat, the steam can easily flow from your skin, through the GORE-TEX, and out of your clothes. But water in rain is totally different from sweat. It's a liquid made up of droplets, each of which contains trillions of water molecules. A single water drop is about 20,000 times bigger than the holes in microporous GORE-TEX, so there's no way it's coming through!

That, then, is the clever little secret of GORE-TEX—one of the most amazing materials in the modern world. But you could say it's actually the clever little secret of water—perhaps the most amazing material of all time!

Artwork: How GORE-TEX can be both waterproof and breathable at the same time.

Further Information

You can read more here:

• GORE-TEX® (a registered trademark of W. L. Gore & Associates).
• Teflon® (a registered trademark of E. I. du Pont de Nemours and Company).