Do You Wear Underwear With Swim Trunks? The Honest Answer

No, you do not wear underwear with swim trunks. The liner sewn inside your trunks is the underwear. It is designed to get wet, dry fast, and provide support. Regular underwear is designed to do none of those things, and wearing it in the water creates exactly the problems you are trying to avoid: soggy fabric, chafing, and a waistband peeking out like it is checking the weather.

That is the short answer. The longer answer has a few exceptions worth knowing, so let's go through it.

Why shouldn't you wear underwear with swim trunks?

Four reasons, all of them learned the hard way by generations of men:

• Cotton and water are enemies. Regular boxers or briefs are usually cotton. Cotton soaks up water, gets heavy, and stays wet for hours. You will be sitting in a damp diaper long after everyone else is dry.
• Wet underwear chafes. Wet underwear rubbing against wet skin is a friction machine. It grinds your inner thighs and groin with every step down the beach.
• Bacteria love it. A warm, damp cotton layer that never dries is a five-star resort for bacteria and fungus. Swamp conditions down there lead to rashes and jock itch.
• Everyone can see it. Wet trunks cling. That waistband and the outline of your boxers are visible to the whole pool. It looks like exactly what it is: a guy who wore underwear in the water.

Your trunks already come with a layer that handles support and coverage. Adding underwear on top is wearing two hats because you do not trust the first hat.

What is the liner in swim trunks for?

That netting or fabric layer inside your trunks is a built-in replacement for underwear. It exists to give you support in the water, keep wet trunks from turning see-through, and dry fast when you get out, because it is built from quick-drying materials, not cotton.

Whether it does that job well is another story. The classic mesh netting is scratchy and traps sand, which is why so many guys either cut it out or hate their trunks. Modern trunks use a soft compression liner instead, which does the same job without the cheese grater feel. Either way, the liner IS the underwear. That is the design.

What material should you wear under swim trunks?

Whatever touches your skin in the water should be a fast-drying synthetic: polyester, nylon, or a nylon-spandex blend. These drying materials shed water in minutes and slide against your trunks instead of gripping your skin. Cotton does the opposite. It drinks water, stays heavy, and turns any layer into a wet rag. That is the whole reason a swim brief or compression short works under unlined trunks and a cotton boxer does not. Simple test: if the tag says cotton, it does not belong in the water.

When is it OK to wear underwear with swim trunks?

There are three honest exceptions:

1. You are not going in the water. Manning the grill, playing beach volleyball, staying dry all day? Then your trunks are just shorts, and normal underwear rules apply.
2. Your trunks have no liner. Some board shorts come unlined. In that case, wear something, but make it a quick-dry compression short or swim brief, never cotton.
3. You need more support than the liner gives. Loose mesh liners offer roughly the support of a screen door. If you are running or playing sports in the water, a proper swim brief or quick-dry compression short underneath is a fair fix.

Notice the pattern: even the exceptions call for swim-specific layers, not the boxers from your dresser.

What should you wear under swim trunks instead?

If you find yourself constantly wanting a layer under your trunks, that is not a you problem. That is a trunks problem. Trunks with a soft built-in compression liner remove the entire question: support, coverage, and quick drying in one garment, no packing extra underwear for the beach.

Frequently asked questions

Do guys wear underwear under swim trunks?

Most do not, and most who do stop after one soggy afternoon. Forum threads on this topic run heavily toward "no, the liner is the underwear." The guys who choose to wear underwear with swim trunks almost always mean swim-specific briefs, not cotton boxers.

Can you wear boxers as swim trunks?

Yes, but it takes forever to dry. Some pools ban them outright for hygiene reasons.

Should kids wear underwear under swim trunks?

Same rules: no cotton underwear in the water. If a kid needs an extra layer for comfort, use a swim-specific liner or compression short. Wet cotton chafes kids even faster than adults.

Do you wear underwear with board shorts?

If they are unlined, wear a quick-dry compression short or swim brief. If they have a liner, skip the extra layer.

Why does my liner feel so uncomfortable?

Because most trunks still use mesh netting, which is a scratchy open weave that traps sand and rubs wet skin raw. See our full breakdown of why swim trunks have that netting and what to look for instead.