Fit Is Where the Warmth Comes From

A wetsuit does not warm you the way a coat does. It lets a thin layer of water in, holds it against your skin, and your body heats it. If the suit is baggy, that layer sloshes about and is replaced with fresh cold water every time you move — the term for it is flushing, and it is the fastest route to a shivering, spoiled swim. This is why fit matters more than thickness. A snug, well-cut 4 mm suit will keep you warmer than a loose 6 mm one on most days.

As a rough guide for UK waters: 2–3 mm suits a warm summer lake or river; 4–5 mm covers late spring, early autumn and cooler summer days; 5/4 mm and above, with a hood, is winter and early spring territory. Sea temperatures lag a long way behind the air, so a July sea can still be a bracing 14°C.

Test Shoulder Mobility Before You Buy

Most wetsuits fail in the shoulders, not the legs. You need to reach forward and overhead without the neoprene dragging you back, so try the suit on dry if you can. A thin base layer or swimsuit underneath helps, and a plastic bag on each foot gets your ankles through without a wrestle. Then work through this:

• Raise both arms straight overhead. Your hands should meet or come close. If your arms stop at ear level, the suit is too tight across the back or the panels are cut too flat.
• Do ten slow imaginary front-crawl strokes. You want slight resistance, not a fight. Any pinching under the arms or across the chest is a dealbreaker.
• Cross your arms and reach for the opposite shoulder blade — this mimics putting on a rucksack or hauling yourself over a rock.
• Squat, stand, and lift a knee to hip height. Check that the crotch does not sag and the knees do not billow.
• Take three deep breaths. If you cannot fill your lungs properly, size up.

Give it five minutes. A suit that feels merely tight in the shop will feel like a vice once you are breathing hard in cold water.

Neck Seals, Wrists and Ankles

The neck is the biggest leak. A good collar sits close against the skin with a smooth, rubbery edge. You should be able to slide two fingers under it — no more, and comfortably. If it presses on your throat or makes swallowing odd, it will only feel worse mid-swim.

Check that the collar does not gape when you look sideways or upwards. Velcro adjusters are handy but can catch long hair; try them before you commit. Wrist and ankle seals should feel firm without restricting circulation — if your hands tingle or go pale, they are too tight. Cuffs that flare and scoop water on entry are nearly as bad as a leaking neck.

Zips matter too. A back zip usually needs a friend to close, but gives a more flexible chest. A front zip is easier on your own and often the better choice for a lone dipper.

Thickness, Seams and Linings

Once fit is settled, use the numbers. Thickness comes as two figures — 4/3 mm, for example, means 4 mm on the torso and 3 mm on the limbs, a sensible balance between core warmth and shoulder freedom. A hood, separate or attached, adds a surprising amount of comfort in water below about 15°C.

Look closely at the seams. Flatlock seams are quick and cheap but tend to leak; glued and blindstitched seams are the sensible minimum for open water, and taped or liquid-sealed seams are better still. Run a thumb along the inside seams — any grit, hard ridges or loose thread will rub you raw after a mile of swimming.

Linings vary, too. Some suits use a thermal or textured lining that traps more warmth without adding bulk; others use stretchier, lighter neoprene that is simply easier to swim in. Neither is automatically better — the one that fits your body and your stroke wins.

Gloves, Boots and the First Cold Minute

Cold hands and feet end swims early. Neoprene gloves, boots and a hood are the cheapest warmth you can buy, and they let you use a thinner suit in the same water.

When you get in, do not dive. Wade to knee depth, splash your face and wrists, and breathe out slowly while your body accepts the cold. That gasp reflex is normal and passes in under a minute. Then swim, staying within your depth and near a known exit — river banks and lake shores look very different from water level.

• Take a tow float: it makes you visible to boats and gives you something to rest on.
• Tell someone where you are going and when you expect to be back.
• Get out while you are still enjoying it. Shivering, clumsy hands or slurred speech mean stop now, not in ten minutes.
• Warm up slowly afterwards with dry layers and a hot drink, not a hot shower straight away.

Care and Buying Second-Hand

Rinse your suit in fresh water after every swim, dry it inside out in the shade, and store it flat or on a wide, padded hanger. Sunlight, heat and petrol fumes all kill neoprene quickly.

Second-hand suits are excellent value, but check for cracking, delamination where the lining lifts away from the neoprene, stiff or perished collars, and a smell of old chlorine or damp. Remember that a used suit has already stretched to somebody else's shape, so be honest with yourself about whether it truly fits. Looked after properly, a good suit will give you several seasons of cold, clear water.