Wetsuits and Drysuits

Why you need a suit

Water conducts heat away from the body roughly 25 times faster than air at the same temperature. Even water that feels warm, around 27°C (80°F), will cool you over a long dive or several dives in a day. Cold makes you tired, uses more air, dulls thinking and is thought to raise the risk of decompression sickness. A suit also protects your skin from scrapes, stings and the sun.

How wetsuits work

A wetsuit is made of neoprene, a rubber foam full of tiny closed gas bubbles. The bubbles insulate you. A thin layer of water gets in between the suit and your skin, your body warms it, and a good fit keeps it from being flushed out. A loose wetsuit lets cold water circulate and loses much of its warmth.

Because neoprene is full of gas, it is affected by Boyle's law. The bubbles shrink as you go deeper, so a wetsuit insulates less at 30 m than at the surface, and it loses buoyancy as it compresses. That's why you need to add air to your BCD as you descend.

Wetsuit thickness guide

Suits are described by their thickness in millimetres, sometimes with two numbers, like 5/4, where the body panels are thicker than the arms and legs. A common rule-of-thumb guide:

People feel cold differently, so treat this as a starting point. Many divers wear a thicker suit than the table suggests, add a hood (a lot of heat is lost from the head) or layer a vest under their suit.

Semi-dry suits

A semi-dry suit is a thick wetsuit, often 6 to 7 mm, with tight seals at the wrists, ankles and neck and a water-resistant zip. It lets in very little water, so it stays warmer than a normal wetsuit and suits cold water when a drysuit isn't available.

Drysuits

A drysuit keeps water out completely, using watertight seals at the neck and wrists, a waterproof zip and attached boots or socks. Warmth comes from the undergarments you wear inside it, so the same suit can work in a wide range of temperatures. Drysuits are made from compressed neoprene or from a thin shell of laminated fabric.

Air inside a drysuit compresses on the way down and expands on the way up, so the suit has its own inflator and exhaust valve, and you control buoyancy partly with the suit. This takes practice, and a drysuit course is strongly recommended before your first drysuit dive. Technical divers breathing helium mixes often inflate their drysuits with argon, which insulates better.

Fit and care

Fit matters more than brand. A wetsuit should be snug everywhere without restricting breathing or movement, with no gaps at the lower back or under the arms. Rinse suits in fresh water after diving, dry them inside out in the shade and hang them on a wide hanger so the shoulders don't crease.

Frequently asked questions