A diver's image is defined by his or her wetsuit. From the stick-thin Jacques Cousteau with his trademark black suit and red woollen hat, to the cutting-edge suits worn by divers working on the recovery of the Russian submarine Kursk, exposure suits are as integral to diving as the basic breathing equipment which started the sport in the 1940s.
Make no mistake, it's easy to get cold even in tropical waters. Water conducts heat away from the body far faster than air. Heat loss is not the only important factor; most wetsuits provide important protection from stinging animals and coral scratches. They can even help with massive, traumatic injuries: the Australian spear-fisherman Rodney Fox was nearly bitten in half by a great white shark, but his tight-fitting wetsuit held him together, preventing his guts from spilling out into the water. He was able to struggle back to shore, and subsequently recovered.
For the very warmest water, light-weight, full-body skins made of nylon and Lycra have become very popular. They look smart, weigh practically nothing, and allow complete freedom of movement. Be warned, however, that these suits are incredibly revealing: pretty much every bump and lump on your body will be evident to fellow divers. Some divers wear Lycra suits under their wetsuits, as an additional layer of insulation.
The wetsuit is by far the most common form of protection, made of closed-cell foam neoprene which provides excellent insulation and reasonable elasticity. Thicknesses vary from 2-5mm for tropical waters to 7-9mm for colder waters. Wetsuits come in various styles: "shorties" only cover the upper legs and torso, ideal for warm summer waters ; one-piece full-body suits provide far more protection. Some suits are two-pieces, with separate jackets and boiler suits. Added insulation comes from rubber bootees and, when chilly, a neoprene hood.
The most important thing is to ensure a tight fit. Your body heats the small amount of water trapped between skin and suit, but if water is allowed to "flush" through the suit, it loses its ability to retain heat. Semi-dry suits have tight-fitting neoprene seals at the ankles and wrists, although some water will still enter through the zip and at the neck.
For temperate waters such as those around the UK, serious divers favour drysuits, which fully enclose the body. Membrane drysuits use a thin, waterproof shell to enclose the body, but offer little insulation in themselves: you keep warm by also wearing purpose-designed garments known as undersuits, the thickness of which can be varied to suit the ambient temperature. Neoprene drysuits can fit tightly like a wetsuit, but the most popular models these days are of a loose fit, in order to accommodate undersuits.
The air inside a drysuit is compressed as you descend, and you lose buoyancy. To counter this, drysuits have valves that connect to the air supply via a low-pressure hose. You press a button on your chest, and air is injected into the suit. As you ascend, the air expands, and can be dumped via automatic valves that open when the arm is raised. Dry suits are more complicated than wet suits, and anybody who wants to buy one should take advantage of one of the short courses offered by diver-training agencies.
Simon Rogerson is assistant editor of "Dive" magazine Next week: football boots
Italian-made full-body 5mm wetsuit; great all-rounder. Ideal for cooler tropical and sub-tropical climes. Shops sell all they can get. Stitching excellent, neoprene high-quality, towelled interior makes them easy to don. Comes with hood and "shortie" which can be worn over full suit for added insulation.
Scubapro SilverSkin Scotia
Most semi-dry suits are at least 7mm, but this 6.5mm model compensates by providing a dry-zip, so less water gets in and body heat is retained better, provided it is a good close fit. Very flexible, but probably best suited to sub-tropical venues like the Mediterranean, South Africa and Canary Islands.
Typhoon Neo T2000
Superb drysuit made from 3mm, high-density neoprene. Incredibly flexible, will keep you warm for a long time when worn with a good undersuit. Tough Kevlar knee-pads offer additional protection in arduous conditions. Automatic air dump, neck seal with neoprene collar for added warmth.
You may look like an extra from "Star Trek" wearing one of these Californian bodysuits, but they do an excellent job in water 26C or warmer. Adequate protection against most jellyfish stings, but sharp coral will easily cut through. One plus of this suit is lightness: it may be possible to descend without a weightbelt.
Price: £99.95Reuse content