Wetsuit Thickness Guide: What to Wear in What Water

Ask a new diver what wetsuit they need and the honest answer is: it depends. The right thickness is the difference between a relaxed, comfortable dive and shivering your way through a safety stop — and getting cold underwater isn’t just miserable, it’s a genuine safety issue. Here’s a clear guide to how wetsuits work, what thickness suits what water, and how to land on the right one for the diving you actually do.

How a wetsuit actually keeps you warm

It surprises people, but a wetsuit doesn’t keep you dry — it keeps you warm. A thin layer of water seeps in and your body heats it, and the neoprene’s job is to trap that warmed layer against your skin and slow the rate at which your body loses heat to the water around you. Thicker neoprene traps more and insulates better; it’s also more buoyant and less flexible. That’s the central trade-off of the whole decision: warmth on one side, flexibility and comfort on the other.

Fit matters just as much as thickness. A suit that’s too loose lets water flush through and flush away the warmth; one that’s too tight restricts your breathing and movement. A wetsuit should be snug all over with no big gaps, especially at the neck, wrists and ankles.

Thickness, water temperature and you

Wetsuit thickness is given in millimetres, sometimes as a single number (5mm) and sometimes as two (5/3mm, meaning 5mm through the core and 3mm at the limbs for flexibility). As a rough, honest guide:

Warm water (roughly 25°C / 77°F and up): a thin suit or a shorty — 2–3mm — is plenty, and many divers wear just a rash guard or skin in truly tropical water. Temperate water (about 18–24°C / 64–75°F): a 5mm fullsuit is the versatile all-rounder most divers reach for. Cold water (below about 18°C / 64°F): a 7mm fullsuit, usually with a hood, boots and gloves — and once it gets properly cold, it’s worth asking whether a drysuit is the better answer.

One big caveat: these are starting points, not rules. How cold you run, how long your dives are, and how many you do back-to-back all shift the maths. If you feel the cold, size up a thickness; you can always vent a little warm water, but you can’t add neoprene at depth.

Here are three suits that map onto those tiers:

Scubapro Men’s 2mm Sport ShortyA light 2mm shorty for warm, tropical water — comfortable, easy to travel with, and just enough to take the edge off.$129.00  ·  View product →

Fourth Element Proteus II 5mm WetsuitA premium 5mm fullsuit and a true all-rounder — the versatile thickness most divers get the most use out of.$804.00  ·  View product →

BARE 7mm Revel WetsuitSerious cold-water warmth at a friendly price — a 7mm fullsuit that, with a hood and gloves, keeps you comfortable when the water turns cold.$419.95  ·  View product →

Don’t forget the extremities

A huge amount of heat escapes from your head, hands and feet, so thickness isn’t only about the suit. In cooler water a hood makes a bigger difference than most people expect, and boots and gloves keep the parts that get cold first comfortable and working. Building your exposure protection as a system — suit, hood, boots, gloves — is what actually keeps you warm, not the suit alone.

Shorty, fullsuit, or build a layering system?

Thickness isn’t the only lever. A shorty covers the core but leaves the arms and legs bare — light, cool and great for warm water or as an extra layer. A fullsuit covers you ankle to wrist and is the everyday workhorse for most diving. And many divers build a small layering system instead of owning a suit for every temperature: a fullsuit plus a hooded vest or a shorty worn over the top adds warmth for cooler trips without buying a whole second suit. If you dive a range of water, two well-chosen pieces often cover more conditions than one very thick suit ever could — and they pack smaller for travel.

Make it last

A wetsuit is an investment, and a little care doubles its life. Rinse it in fresh water after every dive to flush out salt, sand and chlorine; dry it out of direct sun, draped over a wide hanger rather than creased on a thin one; and store it flat or loosely rolled rather than crammed in a bag. Treat the neoprene kindly and a good suit keeps its stretch, its seals and its warmth for years — which is exactly what makes buying the right one worthwhile in the first place.

How to choose yours

Start from the water you dive most, lean warmer if you feel the cold, and get the fit snug and gap-free. Then come try a few on — neoprene fit is personal, and a suit that seals beautifully on one body gapes on another. We’ll help you work through the wetsuits we stock and match thickness, style and fit to your diving, so you’re warm, comfortable and free to enjoy the dive.