by Chris Woodford. Last updated: June 24, 2018.
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't 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.
The perspiration problem
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
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, drift through the
GORE-TEX (by a process called diffusion), 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. Steam caused by perspiration passes out easily because the water molecules are smaller than the pores
in the GORE-TEX liner; water droplets can't get in the other way because they're much bigger.
Two layers are better than one
“I figured that if we could ever unfold those (Teflon) molecules, get them to stretch out straight, we'd have a tremendous new kind of material.”
Wilbert Gore, The New York Times, 1985.
That's a very basic explanation—and if it's all you want to know, you can stop reading now. In practice, things are a
little bit more sophisticated!
GORE-TEX clothes are generally made from three layers: a conventional outer shell fabric, plus two separate GORE-TEX layers with similar but quite different waterproof-breathable properties. On the inside, there's a relatively thin, relatively delicate inner membrane or film that's hydrophilic ("water-loving"), which readily allows water vapor to escape but
doesn't allow liquid water in. The hydrophilic layer absorbs perspiration produced by your body and transports it, by
diffusion, to the outside: unlike with many other textiles, the water doesn't move by
wicking and capillary action (where
the water soaks into the fabric and then channels through it, like water moving up a plant from the roots to the leaves), but because of the difference in water concentration between the inside and the outside.
Next to the inner layer, there's a thicker outer layer made from a microporous plastic polymer, such as Teflon.
This layer is hydrophobic ("water-hating"), which means it resists water from outside, even when it's impacting at high speed or pressure (as in heavy rain) or when the fabric is flexing back and forth (as you walk or run along). The hydrophobic layer doesn't soak up water coming in from the outside (droplets simply "bead" on its surface and stay there, without soaking in), but like the inner hydrophilic layer, it does allow perspiration to escape from the inside by diffusion.
Why have two layers to GORE-TEX instead of one? The outer layer provides protection and support for the inner layer,
but it also provides thermal insulation: it reduces heat loss and helps
to keep you warm. If it's not properly hydrophobic, the outer layer soaks up the rain, which cools the
inner layer and makes your body cold. The two layers work together as a team, keeping water out, keeping heat in,
and allowing perspiration to escape.
Alternatives to GORE-TEX
Photo: Dependable waterproof and breathable textiles are a big selling point for high-performance outdoor clothes. Here's a selection of jackets and waterproof pants I've just pulled from my own home. Like rival materials, Schoeller's quick-drying 3XDRY has a hydrophobic outside and a hydrophilic inside, but they're both incorporated into a single layer, woven fabric. According to Schoeller, the fabric moves moisture so quickly that sweat doesn't have time to build up inside it. That's certainly been my own experience when I've worn the 3XDRY jacket shown here, but as a single layer of fabric it's not so good on colder days. Rohan uses its own waterproof and breathable textile called Barricade™.
GORE-TEX is certainly the best known brand of high-performance, waterproof and breathable textile—but it's
by no means the only one. If you're shopping around for outdoor clothing, bear in mind that there are plenty of rival textiles to
consider; just because it's not branded "GORE-TEX," doesn't mean it's not going to be good.
Two very popular alternatives are eVent and SympaTex. eVent clothing works in a similar way to GORE-TEX:
it has three layers of fabric, with a backing fabric on the inside, a wicking Teflon-type (PTFE) membrane in the middle to draw
moisture away, and a water-repellent outside. SympaTex is quite different.
Instead of having micropores, like GORE-TEX and eVent, it uses what's called a
copolymer, made of hydrophobic polyester and hydrophilic polyether.
The polyester repels water from the outside; the polyether absorbs moisture from the inside and transports
it out, away from your body. But there are no actual pores through which the water travels.
Artwork: A) How SympaTex works: Unlike in GORE-TEX, there are no micropores in SympaTex to carry moisture away from your body. Instead, hydrophilic polyether molecules in the SympaTex membrane effectively act like little "channels," carrying moisture from the inside to the outside.
Artwork: B) Inside a multi-layer aerobic sports garment (such as a waterproof and breathable cycle sweater). 1) On the outside, there's a durable shell made of something like 85 percent polypropylene and 15 percent spandex (to give it body-hugging elasticity). 2) In the middle, there's a layer of waterproof and breathable SympaTex (or GORE-TEX). 3) On the inside, there's a tricot, warp-mesh lining to help moisture wick away from the body and increase comfort.
Quite a few clothing companies have developed their own breathable, waterproof textiles.
Patagonia, for example, has H2No (a two-layer polyester/polyurethane fabric with a water-repellant shell and a breathable membrane);
Rohan has a porous-membrane fabric similar to GORE-TEX, known as Barricade™, and The North Face has a polyurethane coating called DryVent™ (formerly known as HyVent™). Proprietary fabrics obviously have advantages for clothing makers,
who don't have to use and endorse someone else's product or pay their expensive licensing fees. But the
plethora of different options can be very confusing for consumers: which one of these textiles will perform best for cycling, running, day-to-day trips to the office, and so on? Be sure to check out plenty of product reviews
before you buy!
Photo: Keep it clean! One drawback of GORE-TEX is that you need to keep it
clean to keep it waterproof—and clean it properly. Over time, as perspiration from your body escapes out through the
material, it can cause a buildup of surfactants (detergent-like chemicals) that reduces
the effectiveness of the waterproofing. In a similar way, the surfactants in ordinary detergents will
clean GORE-TEX 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.
Who invented GORE-TEX?
In October 1969,
Dr Robert ("Bob") W. Gore (1937–) discovered how to turn PTFE into a microporous material called expanded polytetrafluoroethylene (ePTFE), which makes up the waterproof and breathable membrane used in GORE-TEX. Gore was the son of
Wilbert Lee ("Bill") Gore (1912–1986), a chemical engineer who worked at DuPont before starting his own firm, W.L. Gore & Associates, from his basement in 1957. Initially, Bill Gore's company used DuPont's Teflon to make electrically insulated ribbon cable (parallel connecting cables that link printed circuit boards together inside electronic devices). But it was Bob Gore's discovery of ePTFE that led to real success, spawning all kinds of profitable uses, from waterproof clothing and boots to guitar strings and medical implants, and turning W.L. Gore & Associates into a world-class chemical company with sales of over $2 billion a year.