Choosing a wetsuit, hood and gloves.

Why it matters

DAN's Travelers Medical Guide says water conducts heat away from the body far faster than air, and that even warm tropical water of about 29 to 33 C can cool a person slowly without thermal protection. It defines hypothermia as a core temperature below 35 C, and lists water and air temperature, wind, currents, body composition (leaner and smaller people cool faster), the protection worn, age and health as factors in how fast someone cools. More on environmental hazards.

How a wetsuit keeps you warm: two views

PADI describes wetsuits as closed-cell neoprene, usually lined or coated with fabric, that insulate against cold and guard against scrapes, cuts and stings. On the mechanism the sources differ:

• PADI: water seeps in, the body warms that thin layer and the neoprene insulates it.
• DAN's Alert Diver (Terry Ward, 2012): a wetsuit works mainly by limiting how much water flushes through it, not by warming a trapped layer.

Both views point the same way on fit: PADI says a wetsuit should be snug without being overly tight and with no large gaps, and DAN says beginners often choose suits that are too loose, which lets in more water.

Thickness: the charts disagree

PADI says wetsuits run from 1 mm to 9 mm thick, that thickness is the main factor in warmth, and that 3 mm (warm water), 5 mm (temperate) and 7 mm (cold) are the most common. Labels such as 3/2 or 4/3 give the torso thickness first and the limb thickness second, in millimetres, as the wetsuit maker O'Neill describes them.

Published temperature charts do not line up. Two examples:

A third chart, from Deepblu (seen as a search summary), gives 5 mm for about 18 to 22 C and 7 mm for about 16 to 18 C. Surf charts generally recommend thinner suits than dive charts at the same temperature, and DAN (2012) says dive wetsuits are often thicker than surf suits to offset compression at depth. O'Neill itself calls its chart only a guideline.

Our picks by category

Depth and wear

DAN (2012) says pressure reduces a suit's insulation at depth, and that repeated exposure to depth can thin a suit permanently over time. It also says ultraviolet light and salt water make wetsuits brittle, and recommends a fresh-water rinse and drying in a cool, shaded place.

When a dry suit takes over

PADI describes dry suits as sealing at the wrists and neck to keep water out, for cooler water. We do not pick dry suits, because using one is a skill with its own course:

• DAN's Alert Diver (Michael Menduno, 2012) says dry-suit diving needs training and practice, that most agencies offer dry-suit courses, and cautions against using a dry suit in place of a BCD.
• SSI's Dry Suit Diving standard (2024 standards pages) gives a minimum age of 10, at least one pool or confined water session before open water and at least two open water training dives. PADI's undated Dry Suit Diver course page, seen as a search summary, also gives a minimum age of 10.
• BSAC runs Drysuit Training as a skill development course and says that without its Drysuit Diver card, resorts and dive centres may refuse to rent a dry suit.

See dry suits for the suit types and seals DAN describes, and specialty certifications for the courses.