Wetsuits

Last updated: December 6, 2009.

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 six months of the year. Photo by Andy McKaskle courtesy of US Navy.

How clothes keep us warm

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.

Photo: Heat insulation the natural way! A decent wetsuit should keep you just as warm underwater. Photo of musk oxen on Nunivak Island by courtesy of US Fish & Wildlife Service.

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.

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. Even in the warmest parts of Britain, the water temperature dips to about 8°C (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.

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!

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

How wetsuits work

Put on a wetsuit and everything changes. A wetsuit is made from a synthetic rubber called neoprene and it's designed to fit you very snuggly. As you step into the ocean, a small amount of water seeps into the wetsuit 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 warm water—like a personal, all-over body radiator! Some wetsuits are lined with a thin layer of metal such as titanium and copper to reflect your body heat back inside. That helps to keep you even warmer than a normal wetsuit.

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 parts of the suit are blind-stitched and taped.

For a wetsuit to work properly, the water has to stay inside and stay warm. If a wetsuit fits badly, or water can seep in, the warm water that protects you would constantly drain out and be replaced by cold water from the sea. So 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 elasticated cuffs and legs.

Different types of wetsuits

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: 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!