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Scuba diver in a wetsuit

Wetsuits

by Chris Woodford. Last updated: July 12, 2016.

If you live in a chilly place like the UK or North America, you probably don't set foot in the sea except in summertime. But if you're lucky enough to own a wetsuit, you can swim, surf, or go scuba diving whenever you please. These miracle clothes aren't meant to keep you dry—you get as wet as ever in a wetsuit—but they do keep you safe and warm when the water would otherwise be cold enough to kill. Let's take a closer look at how they work.

Photo: If you're swimming or diving in warm water, you can get away with a "shortie" wetsuit (cut off at the arms and legs) or no wetsuit at all. But if you're planning on surfing, swimming, or diving for more than a few minutes in a colder climate, a full-length wetsuit is a good idea for perhaps 8–9 months of the year. Photo by Andy McKaskle courtesy of US Navy.

How clothes keep us warm

An old blind-stitched Gul wetsuit hanging next to a modern fluid-seam welded O'Neill wetsuit.

Wetsuits are not that different from ordinary, warm clothes—and they work in a very similar way. When you step outside on a chill winter's day, you pile on layers of clothes to keep you warm. You probably know that more thin layers keep you warmer than one thick layer, because several thin layers trap warm air in between them—and it's this air that helps to keep you warm.

How do the layers work? Heat tends to flow from hotter objects to colder ones nearby; that's a basic rule of physics called the second law of thermodynamics ("thermo" = heat, "dynamics" = motion, so "thermodynamics" is the science of how heat moves). Let's say you're standing outside on a winter's morning. If your body temperature is 37°C (98.4°F), and the air around you is just 8°C (46°F), heat flows from your body into the air and your body rapidly starts to cool. It's worth noting that the rate at which your body loses energy is directly related to the difference between your body temperature and the temperature of your surroundings. (That's called Newton's law of cooling.) So the colder the water, the faster you lose energy.

Put on lots of layers and trap warm air in between them and the heat has to flow through a series of warm "airlocks". Air is mostly empty space, so these airlocks are effectively barriers that stop heat escaping. If it's harder for the heat to escape, it's a whole lot easier to stay warm.

Stopping heat from escaping this way is called insulation. We insulate the walls and roofs of our homes for the same reason. Insulation means providing a barrier to stop heat escaping. We often think of ourselves trying to "stop the cold getting in." But there's not really any such thing as cold. Cold is just a lack of heat. What we really mean is that we're trying to prevent the heat from getting out.

Photo: Wetsuits provide heat insulation, but some work better than others. Although both have similar thicknesses of neoprene, the new O'Neill suit on the right is much warmer than the old Gul suit on the left. Where the Gul suit has many body panels and blind-stitching (explained below) to hold them together, the O'Neill has far fewer panels and "fluid-seam welds" (plastic melted on top of the joins) to keep the cold water out. The welds are the shiny gray lines you can see criss-crossing the suit.

Why ocean water cools your body so quickly

Now imagine that instead of standing outside in the cold air, you're swimming in the freezing cold ocean in the middle of winter wearing only a pair of boardshorts! Unless you live in the tropics, the ocean water where you live will get very cold in winter. In a fairly cold, coastal country like the UK, the water temperature dips to about 6–8°C (43–46°F) in February/March, when the sea is at its most bitter. Venture into water that cold without a wetsuit and you risk a life-threatening condition called hypothermia, where the inner "core" of your body gets so cold that it doesn't warm up again. It is very dangerous to swim in water that cold. Your heart stops beating properly and you can die in a matter of minutes.

Bar chart showing year-round coastal sea temperatures for South Central UK.

There's an added problem because water is very different from air. Air is a thin gas, while water is a heavy, dense liquid. So, when you swim, there are far more water molecules surrounding your body. The water molecules are also much nearer to one another, so they can conduct heat more efficiently than air. This is why water carries heat energy away from your body around 25–40 times faster than air. It's also why, on a warm summer's day, you can get in the ocean and feel freezing even when the water and the air are the same temperature: you feel cold because the water is ferrying heat away from your body like a conveyor belt!

Chart: Left: Typical year-round coastal sea temperatures (in °C) for the South Coast of the UK, where I live. There are several things to notice here. First, note how the sea temperature is less than half your body temperature (37°C) all year round—and, in winter, less than a fifth of your body temperature. Notice how the water temperature "lags" behind the ambient, air temperature by about 2–3 months, making September and October reasonably good times to swim even if the air temperature isn't so warm. I go in the water all year round and wear a wetsuit in the blue months. In the dark blue months, I also wear gloves and boots. You can see very clearly from this chart how a wetsuit extends your swimming season from three months to five (if you don't care for gloves and boots) or twelve (if you do). Even if you miss out the worst months (December through February), you can still comfortably swim nine months of the year with a wetsuit. "Comfortably," is of course a subjective word.

How does a wetsuit work?

What's so good about neoprene?

Put on a wetsuit and everything changes. A wetsuit is made from multiple layers and, most importantly, a thick layer of synthetic rubber called neoprene. If you're interested in chemistry, neoprene is the generic name for an organic (carbon-based) chemical called polychloroprene, which is a polymer (a very large molecule made from endlessly repeating building blocks called monomers), typically built from the monomer 2-chloro-1,3-butadiene. Unless you're a chemist, that will mean nothing and you won't care! The really important thing about neoprene is that it's a kind of foam rubber with a cellular structure that has nitrogen gas bubbles trapped inside it, which make it a particularly good heat insulator.

Layers, layers, layers!

How a wetsuit works with multiple insulating layers between your body and the sea.

Most wetsuits are made from multiple layers—and these help to trap and reflect heat much like any other insulating clothes. Some are lined with a thin layer of metal such as titanium or copper to reflect your body heat back inside. That helps to keep you even warmer than a normal wetsuit. Also, as you step into the ocean, a small amount of water seeps in between the neoprene costume and your skin—and stays there. Your body quickly warms this water up to something approaching normal body temperature. So now, between you and the sea, there's an insulating layer of rubbery material, some warm water, and multiple layers of insulation—all working together like a kind of personal, all-over body radiator! Not all wetsuits are the same, but these layers are typical of what you might find between your warm body and the cold sea:

  1. Your own skin.
  2. A thin layer of trapped water warmed by your body.
  3. A layer of nylon or some other comfortable fabric to stop the neoprene rubbing and chafing your body.
  4. A thin layer of heat-reflecting material based on a metal oxide of titanium, copper, silver, magnesium or aluminum.
  5. A thick layer of neoprene containing trapped bubbles of nitrogen. This is the most important part for keeping you warm.
  6. A durable outer layer made from some water- and abrasion-resistant material.

Keep that water out!

For a wetsuit to work properly, any water that seeps in has to stay inside and stay warm. If a wetsuit fits badly, or isn't well sealed, the warm water layer will constantly "flush" in and out and be replaced by cold water from the sea—which, if you think about it, would be almost the same as wearing no wetsuit at all. As wetsuit inventor Hugh Bradner (see below) first realized, a neoprene wetsuit keeps you warm in spite of the fact that it makes you wet, not because of it. Even so, stopping cold water from flushing in and out is vital. That's why the seams of a wetsuit (where the separate panels of neoprene are joined together) are held together with special waterproof tape. They are also "blind-stitched": instead of the stitch holes going all the way through, they go only part of the way through the neoprene from the inside. That means there are no stitch holes in the outside of the neoprene to let in cold water. For the same reason, wetsuits have tight-fitting cuffs and legs.

Brass zip on Gul blue and black wetsuit Wetsuit blind stitching and taping

Photo: Left: A tough brass zip and thickened rubber flaps keep water out of the back of this winter wetsuit. Right: This is what a wetsuit looks like inside. The outer neoprene is lined with smooth nylon (which feels better on your skin). The seams of the suit are blind-stitched and taped to stop cold water getting in and warmed water getting out.

Different types of wetsuits

Gul blue and black winter, steamer wetsuit

Wetsuit boots and fin socks

Different wetsuits are available for different conditions. They come in different thicknesses of neoprene to suit different times of year and you can get "steamers" (full-length suits that cover your entire body), "shorties" (which have short sleeves and legs), or just vests and trunks. For total winter protection, you also need neoprene gloves, boots, and sometimes even a neoprene hood.

All this gear might look downright weird, and it can take a while to put it on and take it off, but once you're inside, you're ready for anything the ocean can throw at you—even in winter!

Photo: Left: A typical winter "steamer" wetsuit has an upper chest section made of neoprene 5mm (0.2 in) thick. The rest of the suit is made from thinner, 3mm (0.1 in) neoprene.

Photo: Right: For cold water "work," you'll need neoprene boots and gloves too. Here we have some surfing boots (bottom), made from titanium-lined neoprene with thick polypropylene soles so you can get good grip on your board and also walk around without wearing them out. Above them are some neoprene fin socks, also lined with titanium, which are designed to be worn inside fins (flippers) when you're bodyboarding. They're similar to the boots (and just about as warm), but don't have the thick soles (just a small polypropylene heel). The positive side is that they're very much more flexible; the downside is that they wear out very quickly on the beach and the pier, so take them off once you get out of the water or you'll soon find them in holes!

Who invented wetsuits

Thomas Aud's waterproof diving suit from 1929

Harvey Williams' early diving suit from 1947

Most histories of surfing and diving credit this superb invention to Hugh Bradner (1915–2008), a University of California at Berkeley physicist who developed the idea in 1951 while working for the US Navy. Dr Bradner was responsible for the modern-style neoprene wetsuit—but he didn't invent neoprene (that was one of the synthetic fabrics developed by Wallace Carothers, pioneer of nylon) or come up with the idea of an insulated suit you can wear to save your life in the water.

Four years before Bradner's invention, on January 31, 1947, Harvey L. Williams of Hadlyme, Connecticut filed a patent application (US Patent 2,582,811: Garment) for a "one-piece, step-in and slip-over-the-head" diving suit with elaborate mechanisms to keep the water out and multiple layers to keep the diver warm—and, as Williams' patent notes, there were earlier suits too.

The earliest example of a waterproof diving suit I've found is US Patent 1,706,097: Life-saving suit, filed on February 23, 1927 by Thomas Edgar Aud of Herndon, Virginia. Much more like a modern dry-suit than a neoprene wetsuit, it was "made of some suitable strong and durable water-proof material, such as soft vulcanized rubber or any suitable combination of rubber and fabric" and designed as "a suit for life saving, swimming, and analogous purposes, which may be applied with great ease and speed and which will effectively seal the entrance opening against the intrusion of water." It's important to remember that inventors like Aud didn't have access to neoprene, which was only discovered in 1930.

Where Hugh Bradner deserves real credit is for figuring out that the cellular structure of neoprene makes it a superb wetsuit material. Like many great inventors, he chose not to patent his idea, wrongly believing that only a few hundred people might wear wetsuits. How wrong he was! His invention made it possible for millions of people to take up cold-water sports such as year-round surfing, swimming, and diving. Many people got rich off the back of this great idea, but Hugh Bradner's reward is ultimately greater: his name will always be honored as the inventor of the wetsuit.

Artworks: Early diving suits by Thomas Aud (left) and Harvey Williams (right) courtesy of US Patent and Trademark Office.

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Woodford, Chris. (2007) Wetsuits. Retrieved from http://www.explainthatstuff.com/howwetsuitswork.html. [Accessed (Insert date here)]

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