GORE-TEX®
Last updated: March 12, 2007.
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 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?
A pair of 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
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 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: 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.
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!
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).
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