Why wear a suit?
Water conducts heat 25 times more efficiently than air. That’s why water is usually used to conduct heat in central heating systems. Your body makes heat to maintain your own body temperature. Water will conduct this heat away from you much quicker than if you were in air of the same temperature. This means that you will get cold after prolonged immersion in any water that is colder than your own body. Divers stay totally submerged for long periods at a time. In hot climates, although a dip in the sea will initially be refreshing for a swimmer, for scuba divers, it will soon make them cold. For this reason, divers normally wear a suit for thermal protection.
Wetsuits
Wetsuits are usually made of neoprene. They are called wetsuits because divers get wet when they swim underwater wearing one. However, the layer of water between the diver and the suit is warmed by the body and, provided it doesn’t get flushed out with cold water, it helps keep the diver warm. Of course, the thicker the material of the suit and the more of the body covered, the warmer it keeps the diver. So a 3 mm (1/8 inch) thick ‘shortie’ without arms or legs will not be as warm as a 5 mm (3/16 inch) one-piece, and that will not be as warm as a 7 mm (1/4 inch) suit that has a hood and is worn with a 7 mm (1/4 inch) jacket over top. It’s a matter of layering thermal barriers to suit the conditions. View more wetsuits on this site.
People are different, too. A small, compact person with a thick layer of epidermal fat will tend to lose heat more slowly than someone who carries very little fat. Different body types mean divers will choose to use different suits for the same conditions.
Semi-dry suits
Semi-dry suits really are semi-wet. They have smooth skin seals at the wrist, ankle and collar to stop water flushing in and out. They also have a smooth skin flap behind the zipper for the same reason. However, water does get in but in reduced quantities, and often divers can feel warmer in a good, well-fitting semi-dry suit than in a wetsuit. Some suits have thicker neoprene in areas that do not need to be flexible, combined with lighter weight neoprene at joints like elbows and knees.
When choosing a suit, get one that fits you. To work well, a wetsuit should be a good fit, although modern super-stretch neoprene makes this less of a problem than it used to be. Female divers will want a suit that is specifically designed for their shape. The designers of wetsuits have recently woken up to the fact that most women have a different shape from men!
A full suit protects the wearer from abrasions caused by accidental contact with rocks, coral or the rusting metal of shipwrecks, and it prevents stings from plankton and jellyfish.
What to wear when and where
If you dive in temperate waters, such as those found in northern California in summer, the Mediterranean in winter, or southern Australia and New Zealand all year round, you will need to have the full protection of a 7 mm (1/4 inch) full-length semi-dry suit with 7 mm (1/4 inch) jacket worn over it. The Red Sea and the seas around South Africa in winter require a 7 mm (1/4 inch) full-length semi-dry suit. A 5 mm (3/16 inch) full-length semi-dry suit is suitable for diving in the Mediterranean in summer, the eastern Pacific, northern Australia and places that are swept by strong ocean currents. A 3 mm (1/8 inch) full-length wetsuit is fine for the Caribbean, the Red Sea in summer and waters in most tropical zones that are not subject to strong currents.
