Wetsuits: thickness, fit and the charts that disagree.

What a wetsuit is for

PADI describes the wetsuit as exposure protection: it insulates against cold water and guards the skin against scrapes, cuts and stings. Suits are made of closed-cell neoprene, usually lined or coated with fabric. DAN's Alert Diver (Terry Ward, 2012) adds that dive wetsuits differ from surf suits in how the arms and shoulders are cut, and are often thicker to make up for compression at depth.

How it keeps you warm: two explanations

PADI and DAN describe the mechanism differently.

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

Both agree that fit matters. PADI says a suit should be snug without being overly tight, with no large gaps. DAN adds that beginners often choose suits that are too loose, which lets more water in.

Thickness and what the numbers mean

PADI says wetsuit thickness runs from 1 mm to 9 mm and is the main factor in warmth. It names 3 mm, 5 mm and 7 mm as the most common, linked broadly to warm, temperate and cold water. DAN says warmth also depends on the density of the neoprene and on how well the suit seals at the wrists, ankles and chest. Carbon black is added to neoprene for strength and resistance to sun, according to DAN.

Two numbers on a label, such as 3/2 or 4/3, give the torso thickness first and the arm and leg thickness second, in millimetres, as wetsuit maker O'Neill describes its labelling.

Depth reduces insulation

DAN (2012) says pressure reduces a suit's insulation at depth, and that repeated trips to depth can thin a suit permanently over time.

Styles and features

PADI lists four styles: one-piece, two-piece, shorty and semi-dry. A shorty has short sleeves and legs that end at the thigh or knee. Optional features PADI names include an attached hood, which stops cold water flowing in at the collar, wrist and ankle seals, spine pads and knee pads.

PADI says a wetsuit should last several years, and that custom suits are made for divers whom nothing off the shelf fits.

Temperature charts: they do not agree

Retailers and makers publish charts pairing water temperature with suit thickness. They differ by several degrees, and surf charts suggest thinner suits than dive charts at the same temperature. None of them is a rule. Two are shown here so the spread is visible.

A third chart, from Deepblu (seen in a search summary), puts 5 mm at about 18 to 22 C and 7 mm at about 16 to 18 C, so even the dive charts disagree with each other. O'Neill itself calls its chart only a guideline, and Divernet's chart is labelled as content marketing produced with a dive retailer.

Care

PADI says to rinse, dry and store a wetsuit after each dive, wash it occasionally with wetsuit soap and hang it on a wide hanger. Its 2015 list of things that damage gear says never to put a wetsuit in a washing machine or tumble dryer, and to dry it in shade, inside out as well as outside. DAN (2012) says sunlight and salt water make neoprene brittle. More on this is on care and storage. Colder water than a wetsuit suits is covered on dry suits.