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Wetsuits are a scuba diving item that serves two main functions. A wetsuit helps to control a diver’s temperature. It also protects a diver from incidental abrasion against underwater features that could cut the skin, such as coral or rock. Their primary purpose is the first one, temperature control.
So, why do divers wear wetsuits in all diving? After all, balmy tropical oceans won’t cause you to freeze to death, right? The answer to that is not the resounding “yes” you’d expect, but rather a tepid “mostly not.” You see, water is very different than the air we spend most of our time in. you’re probably saying “well yea, that’s why we can’t breathe it” about now, and you’re spot on in that assessment. But there is more to it than that.
For one thing, water reacts to light differently than air. When a beam of light passes through matter, several things can happen. First, the matter can absorb the light, that is where colors come from. Certain matter absorbs all but a specific bandwidth of light, and what we see as color is the light that got away. The second thing that can happen is that the matter can reflect it. We see this happening in mirrors. The observant among you will note that still water can act as a mirror, so water has this property. The third thing that can happen is that the matter can deflect the light from its original course. This is called refraction, it’s what a prism does to create the spectrum of light we see coming out of it.
The last two are properties of both water and air. However, water is far more reflective and far more refractive than air. What does that have to do with wetsuits? Well actually, nothing, but it illustrates how fundamentally different water and air can be. Another difference between water and air is thermal conductivity. Thermal conductivity is a measurement of how well a material transmits heat. It is often closely linked with electrical conductivity. Metals are usually among the best thermal and electrical conductors around. But hey, what about water and air?
Air, contrary to popular belief, is a poor conductor of both electricity and heat. Air can reflect heat well, hence the greenhouse effect. But it doesn’t actually transfer heat very effectively. For instance, it would be far more efficient to heat and cool the walls and floor of your house than it is to pump hot or cold air through the open spaces between them. We don’t do this because it’s more expensive and troublesome to install heating and cooling systems in the walls and floor, but it would be a more effective use of technology. Lightning is another great example. Lightning has to build up a charge of several hundreds of thousands of volts before it can overcome air’s resistance to transmission and make it to the ground.
Water on the other hand is a much better conductor of both heat and electricity. That’s why you should never bathe with your toaster, it’ll kill you! But wetsuits, wetsuits, how does this tie in with them? Simply put, water conducts heat very well, so it conducts the heat of your body away, into the cooler surrounding water. Well there’s a lot more water than there is you, so your body is effectively trying to heat the ocean to 98.7 degrees. Needless to say that’s a futile effort, which can actually lead to hypothermic shock in even relatively warm waters.
How do wetsuits solve this problem? Well a wetsuit is a thermal insulator rather than a thermal conductor. So it doesn’t transmit heat. The wetsuit absorbs water, trapping a thin layer against your skin. This thin layer of water is heated to your body temperature, but is prevented from leaking into the outside water because of your suit. It effectively provides two forms of insulation for your body, keeping it at a constant temperature while you dive.