Exposure suits and thermal protection

In short

Water cools the body much faster than air, even when it feels warm. An exposure suit limits this heat loss: a wetsuit for temperate and warm water, a semi-dry or dry suit for cool and cold water. Hood, gloves, boots and surface protection complete the set. Cold is not just a matter of comfort: it tires you, increases your air consumption and reduces your alertness. Cut a dive short as soon as you start to feel cold.

Why it matters

A cold diver breathes faster, tires, handles equipment less well and makes poorer decisions. Cold is also considered a contributing factor in several diving accidents. Choosing the right thermal protection therefore makes diving both more pleasant and safer.

Why you get cold underwater

Water conducts heat about twenty-five times better than air. At the same temperature, the body therefore loses heat much faster in water. Several mechanisms add up:

• conduction: heat passes directly from the skin to the water;
• convection: water moving around the body carries heat away, all the more when it is renewed (current, finning, a suit that is too loose);
• breathing: the dry, expanded air from the cylinder is warmed and humidified in the lungs, which also costs heat.

Water at 26 °C feels warm at the start of a dive but can make you cold after an hour, especially when diving several days in a row.

Exposure suits

Wetsuit

A thin layer of water between the skin and the neoprene is warmed by the body; the neoprene, full of small gas bubbles, insulates. A wetsuit is simple, flexible and affordable. Its limits: water is renewed if the suit is too big, and neoprene compresses with depth, which reduces insulation.

Semi-dry suit

A thick wetsuit whose seals, zips and seams greatly limit water entry. It suits cool water.

Dry suit

It keeps the diver dry; insulation comes from the undergarments worn underneath and the air the suit contains. It requires specific training: you must manage the air volume in the suit during descent and ascent, and know how to react to an air bubble moving to your feet.

Indicative thicknesses

These figures are only a guide; sensitivity to cold varies a lot from one person to another.

Water temperature	Common protection
Above 26 °C	Shorty or 3 mm full suit
22 to 26 °C	3 to 5 mm full suit
16 to 22 °C	5 to 7 mm full suit, hood
10 to 16 °C	7 mm or semi-dry, hood, gloves, boots; dry suit depending on duration
Below 10 °C	Dry suit with suitable undergarments

Accessories

• Hood: a significant share of heat is lost through the head and neck.
• Gloves and boots: they also protect against cuts and stings.
• Thermal undergarments: under a wetsuit, a thin layer adds warmth; under a dry suit, they provide the insulation.
• Surface protection: windbreaker, poncho or towel between dives. Wind on a wet suit cools you down very fast.

Effect on weighting and buoyancy

Neoprene floats: the thicker it is, the more weight you need. With depth, its bubbles compress, the suit loses volume and the diver becomes less buoyant; you compensate with the BCD. On the way up, the effect is reversed. A new suit or a different thickness means redoing your weight check: see the weighting guide.

Recognising cold and reacting

The first signs are often subtle: shivering, numb fingers, less precise movements, wanting to cut the dive short.

• Signal it to your buddy or guide with the "I'm cold" signal agreed at the briefing.
• Cut the dive short: carrying on will only make things worse.
• After the dive: take off the wet suit, dry yourself, cover up and get out of the wind.
• Do not dive again until you have warmed up.

Intense and prolonged cold can lead to hypothermia; the diving accidents guide explains how to prevent and recognise it.

Key takeaways

• Water cools the body much faster than air.
• Choose protection suited to the temperature and the duration, and a well-fitting suit.
• A thick suit needs more weight; redo your weight check if you change suits.
• A dry suit requires specific training.
• Cold: signal it and cut the dive short.

Further reading

During a dive, the watch shows the water temperature; the recorded session keeps the measured temperatures, which helps you choose your protection for the next dive at the same site. The guides on weighting and on diving accidents complement this one.