The numbers on a wetsuit label aren't random. They tell you exactly how much insulation you're getting — and where. Once you understand the system, choosing the right thickness takes about 30 seconds. Before that, it takes about 45 minutes of confused staring in a shop.
Let's make it 30 seconds.
What do the numbers actually mean?
A wetsuit labelled 4/3mm has 4mm of neoprene in the torso (chest, back, core) and 3mm in the arms and legs. The thicker section goes where you lose the most heat — your core. The thinner sections go where you need the most flexibility — your limbs.
How to read a wetsuit label
4/3mm
4mm torso · 3mm arms & legs
Most common all-round suit
3/2mm
3mm torso · 2mm arms & legs
Warmer water, more stretch
5/4mm
5mm torso · 4mm arms & legs
Cold water, serious warmth
2mm
Single thickness throughout
Warm water, maximum flex
Which thickness for which temperature?
This is the chart the raccoon wishes someone had shown him before he bought a 5/4mm suit for a summer trip to Portugal.
| Water temp | Thickness | Type | Where |
|---|---|---|---|
| 24°C+ (75°F+) | No suit / rashguard | — | Tropics, summer Med |
| 22–24°C (72–75°F) | 1–2mm / Shorty | Shorty or thin fullsuit | Canaries, summer Portugal |
| 18–22°C (64–72°F) | 3/2mm | Fullsuit | Portugal spring/autumn, Morocco |
| 14–18°C (57–64°F) | 4/3mm ⭐ | Fullsuit | Portugal winter, France, Spain Norte |
| 10–14°C (50–57°F) | 5/4mm | Fullsuit + hood | UK, Ireland, Brittany winter |
| Below 10°C (50°F) | 6/5mm | Hooded fullsuit + boots + gloves | Scandinavia, Baltic, Iceland |
⭐ 4/3mm is the world's most popular wetsuit thickness — covering the widest range of conditions.
The Raccoon's Rule #2
When in doubt, go thicker. You can always unzip a 4/3mm if you get warm. You cannot add a millimetre of neoprene you don't have. Cold water ruins sessions. Slightly warm water does not.
Does your activity change which thickness you need?
Yes — and it's often overlooked. When you're moving constantly (surfing, kitesurfing, wingfoiling), your body generates heat. When you're stationary (waiting for waves, diving, cold water swimming), you lose heat fast.
High activity 🏄
Surfing, kitesurfing, wingfoil, SUP — you generate heat. Can often go 1mm thinner than the temperature suggests.
Low activity 🤿
Diving, snorkelling, cold water swimming — you stay still. Go 1mm thicker than the temperature suggests.
Does neoprene quality affect how warm the suit is?
Yes — significantly. A premium 4/3mm suit made from Yamamoto limestone neoprene will keep you warmer than a budget 4/3mm made from standard petroleum neoprene, even at the same stated thickness. This is because higher-quality neoprene has better cell structure, retains warmth more effectively, and stays flexible so you move more — which also generates body heat.
In practice: if you're on the border between two thicknesses, investing in better neoprene can tip the balance. A quality 4/3mm can often perform like a budget 5/4mm.