The short answer
For most surfers in a full suit: board shorts or a swimsuit, or nothing. For cold water: a thermal rash vest under the suit makes a bigger difference than most people expect. For anyone in a hire suit: wear something.
The reason there is no single right answer is that a wetsuit does not work like clothing. It traps a thin film of water against your skin and your body warms it. Anything you put between your skin and the neoprene either helps hold that film in place or gets in the way of it — and bulky, absorbent fabric definitively gets in the way.
What men wear under a wetsuit
- Board shorts — the default, and fine as long as they are thin and have no bulky waistband or pockets. Fitted, quick-dry ones. Baggy shorts bunch up under the suit and chafe.
- Fitted swim briefs or trunks — less bulk, less bunching, warmer. What most regular surfers move to eventually.
- Neoprene shorts — an extra layer of warmth around the core in cold water, and they stop rash on the thighs.
- Nothing — genuinely common, and marginally the warmest option since nothing disrupts the water film. The obvious trade-off is changing on a public beach and hire suits.
What women wear under a wetsuit
- A one-piece swimsuit — the most popular choice. Smooth, no loose straps, nothing to dig in.
- A fitted bikini — works, but check for thick ties or knots at the back of the neck and the spine. Anything with a knot under a wetsuit turns into a pressure point within an hour.
- A sports bra plus swim bottoms — good support, though seams and clasps can rub. Choose a seamless one if you can.
- A thermal rash vest — the single best cold-water addition, and it sits well under a suit.
- Nothing — also common and perfectly fine, with the same practical caveats about changing.
Cold water: what actually helps
Once you are into 4/3 and 5/4 territory, what you wear underneath stops being about comfort and starts being about staying in the water longer.
A thermal rash vest is the best value warm layer in surfing. A thin poly or merino top under a 4/3 buys you a genuine extra half hour in winter, costs a fraction of a thicker suit, and does not restrict paddling the way stepping up a thickness does. If you are cold in a 4/3, try this before buying a 5/4.
Neoprene shorts or a vest add warmth over the core specifically. Useful if your torso gets cold before your limbs do, which is most people.
What does not help: layering ordinary clothing. It absorbs water, holds it cold against your skin and adds bulk that lets more sea flush through. Read the thickness guide if you are cold — the suit is usually the problem, not the layers.
What not to wear
- Cotton anything. It soaks, holds cold water against your skin and never dries. This includes cotton underwear, which is the most common mistake among first-timers.
- Thick waistbands, zips, buttons or knots. Under neoprene pressure these become hot spots, then rash, then a raw patch you feel for days.
- Baggy shorts. They bunch, ride up and chafe.
- Regular underwear. Same problem as cotton, plus seams in exactly the wrong places.
On hire suits: always wear something. It is a shared garment, and this is the one situation where going without is a genuinely bad idea rather than a preference.
Stopping neoprene rash
Neck rash is the most common complaint, and it comes from the collar rubbing wet skin over a long session. A thin rash vest with a smooth collar fixes it. So does a smear of barrier balm or even lip balm on the neck before you paddle out — cheap and surprisingly effective.
Underarm and inner-thigh rash is usually a fit problem rather than a layering one. If the suit is loose enough to move against you there, it is loose enough to flush cold water too — worth checking against the size chart.
Frequently asked questions
Do you wear anything under a wetsuit?
It is entirely optional in your own suit. Most surfers wear board shorts, swim briefs or a swimsuit for comfort and for changing on the beach, and plenty wear nothing at all. In a hire or shared suit, always wear something.
Do you wear underwear under a wetsuit?
Not ordinary underwear. Cotton soaks up water, holds it cold against your skin and its seams cause rash under neoprene pressure. If you want a layer, use swimwear or a thin quick-dry base layer designed for water.
Is it warmer to wear nothing under a wetsuit?
Marginally, yes. A wetsuit warms a thin film of water held against your skin, and bare skin holds that film most effectively. The difference is small though — far smaller than the difference a thermal rash vest makes in cold water, which adds insulation rather than just avoiding disruption.
What do you wear under a wetsuit in cold water?
A thermal rash vest, in poly or merino. It is the best-value warmth upgrade in surfing — a thin top under a 4/3 buys a genuine extra half hour in winter for a fraction of the price of a thicker suit, and it does not cost you paddling flexibility.
What should women wear under a wetsuit?
A one-piece swimsuit is the most popular choice because it is smooth with nothing to dig in. A fitted bikini works too, though thick ties or knots at the neck and spine become pressure points over a long session. In cold water, a thermal rash vest under the suit is the best addition.
How do you stop wetsuit neck rash?
Wear a thin rash vest with a smooth collar, or put barrier balm on your neck before paddling out. Neck rash comes from the collar rubbing wet skin over a long session, and either fix works. Persistent rash elsewhere usually means the suit is too loose rather than that you need more layers.
Next steps
- Wetsuit thickness guide — if you are cold, start here rather than with layers.
- Wetsuit size chart — a loose suit flushes, and no base layer fixes that.
- Surfboard volume calculator — work out your board's litres.