What to Wear Under Swim Trunks? The Honest Answer Most Guys Need to Hear

May 10, 2026

Stop wearing underwear under your swim trunks. Boxers and briefs trap water, cause chafing, and slow down drying — the real fix is a swim short with a proper built-in liner, not an extra layer underneath.

It's one of those questions most guys Google privately but never ask out loud: what am I actually supposed to wear under my swim trunks?

It's a fair question. The first time you try on a pair of swim shorts and feel that thin mesh netting inside, the instinct is to throw on boxer briefs for backup — it feels like the safe move. But wearing underwear under swimwear is almost always the wrong call. It creates more problems than it solves. The real fix isn't another layer; it's choosing the right swim shorts in the first place.

Why Most Guys Wear Underwear Under Swim Trunks

Start with the "why," because it's completely understandable. Most men reach for underwear under their swim shorts for one of a few reasons:

The liner feels cheap. Old-school mesh netting is scratchy, unsupportive, and feels like it's working against you.
They want more support. Especially for active swimming, volleyball, or chasing kids around.
Chafing anxiety. Sand, salt, and repetitive movement can turn a beach day into an uncomfortable ordeal.
Modesty concerns. Some swim trunks are thinner than expected, and nobody wants to worry about transparency when wet.

All legitimate concerns. But the solution isn't layering regular underwear underneath — it's better swim shorts.

Why You Should Never Wear Underwear Under Swim Shorts

Wearing boxers, briefs, or boxer briefs under your swim trunks sets off a chain reaction of discomfort that gets worse as the day goes on.

1. Cotton Underwear Absorbs and Holds Water

Cotton is built to absorb moisture — great for a normal day, terrible in the water. It soaks up water like a sponge and holds onto it for hours. Even if your swim shorts themselves dry quickly, the layer underneath stays damp, heavy, and clingy.

2. It Creates Friction and Chafing

Wet fabric layers rubbing against each other — and against your skin — is a recipe for chafing. Regular underwear isn't seamed for wet, sandy conditions, and movement (walking, sitting, swimming) turns that into irritation that can ruin an afternoon.

3. It Slows Down Drying Time Dramatically

Quick-drying performance is one of the most useful features of modern swim shorts, but even the fastest-drying outer fabric can't overcome a soaked cotton layer underneath. You cancel out the engineering of the outer fabric by adding a slow-drying base layer.

4. Hygiene Issues

Trapped moisture in a warm environment is a breeding ground for bacteria and fungal growth. Damp underwear under swim trunks for extended periods isn't just uncomfortable — it's genuinely unhygienic.

5. It Looks and Feels Bulky

An extra layer adds bulk around the waistband and thighs, which works against the clean line of a well-tailored pair of swim shorts. If you've invested in a modern, streamlined fit, underwear underneath undoes the look.

The Real Answer: Find Swim Shorts With a Great Liner

Instead of layering underwear underneath, invest in swim trunks with a built-in liner that actually does its job. A good liner replaces the need for any undergarment — it provides support, prevents chafing, and dries fast, without the downsides of an extra layer.

Not all liners are created equal, though. Here's the breakdown.

Traditional Mesh Netting

The scratchy, loosely woven net found in most budget swimwear. It technically provides a barrier, but offers minimal support and can irritate the skin. It's a big part of the reason so many guys started wearing underwear underneath in the first place.

Verdict: Better than nothing, but barely.

Compression Liners

Compression liners — similar to built-in bike shorts — have become popular in recent years. They offer solid support and eliminate chafing concerns, but come with a tradeoff: they absorb a lot of water and take a long time to dry. If you want swim shorts that transition from water to lunch to evening plans, a compression liner works against you.

Verdict: Great support, terrible drying time. Not ideal for all-day wear.

Ultra-Fine Micro-Mesh Liners

This is the sweet spot. Ultra-fine micro-mesh liners provide secure, comfortable support while allowing maximum airflow and near-instant water drainage. They don't trap water, they don't cause chafing, and they dry almost as fast as the outer fabric.

Verdict: The best option for comfort, support, and quick-drying all-day performance.

What to Look for in All-Day Swim Shorts

Choose the right pair, and the "what do I wear underneath?" question disappears entirely. Here's the checklist:

Ultra-fine micro-mesh liner. Non-negotiable for all-day wear. It should feel light and almost invisible — support without bulk or trapped moisture.
Quick-drying outer fabric. Look for a tight weave with fine yarns, which keeps water from lingering between fibers and speeds up drying time considerably.
Soft-touch material. Fabric that feels stiff or scratchy when dry will feel worse when wet and covered in sand. Look for fine yarns that feel smooth against skin from the first wear, with no break-in period.
Tailored fit. A modern cut around a 5-inch inseam sits comfortably without excess fabric bunching up — less friction, less water retention, cleaner look.
Salt water and chlorine resistance. If you're swimming regularly, the fabric needs to hold its color and texture over repeated exposure.

Our Take: What This Looks Like in Practice

Blauw's swim trunks were built around exactly this problem. The OceanKnit™ fabric — made from recycled marine plastic in partnership with SEAQUAL — is soft against the skin, dries quickly, and holds a clean structure even outside the water. The built-in micro-mesh liner provides breathable, chafe-free support without the slow-drying downsides of a compression liner, and the tailored 5-inch inseam keeps the fit clean rather than baggy. You can browse the full quick-dry swim trunks lineup to compare fits and colors.

How Other Options Compare

For context, here's how a couple of well-known alternatives stack up:

Patagonia Baggies (5-Inch): A solid, well-known option with quick-drying recycled nylon fabric and a relaxed fit. The liner is functional, though not as refined as a micro-mesh design. A reasonable choice if you prioritize brand familiarity and a slightly looser cut.

Outerknown Nomadic Volley Shorts: Made with recycled materials and a comfortable elastic waist, with a clean, surf-inspired look. Good for casual beach days, though the fabric doesn't dry quite as fast as a tighter-weave construction.

Both are reasonable options if you're comparing across brands — the differences mostly come down to liner refinement and how quickly the outer fabric sheds water, which matters most if you're planning to wear the shorts for a full day rather than just a swim.

The Bottom Line

Stop wearing underwear under your swim trunks — it isn't solving the problem, it's making it worse. The actual fix is a pair of swim shorts with an ultra-fine micro-mesh liner, quick-drying fabric, and a tailored fit that works for your entire day. Get those three things right, and you get all the support and coverage you need without any of the downsides of an extra layer.

Morning walk. Ocean swim. Beachside lunch. Evening drinks. One pair of shorts, zero underwear — that's how it should work.

Key Takeaways

Never wear cotton underwear under swim trunks. It traps water, causes chafing, slows drying, and creates hygiene issues.
The real solution is a better liner. Ultra-fine micro-mesh liners provide support, breathability, and rapid drainage without the downsides of compression or traditional mesh.
Quick-drying fabric matters. A tight weave with fine yarns sheds water in minutes, not hours.
Invest in all-day swim shorts. The right pair eliminates the need for underwear entirely.

Frequently Asked Questions

Can I wear compression shorts under swim trunks instead of underwear?

You can, but it's not ideal for all-day wear. Compression shorts provide good support, but absorb and retain water, leaving you with a heavy, damp layer for hours. A built-in ultra-fine micro-mesh liner gives you support without that slow-drying downside.

Why do swim shorts even have liners?

Liners serve as a built-in undergarment that provides support, reduces chafing, and adds modesty. A quality liner eliminates the need to wear anything underneath, which is exactly how swim shorts are designed to be worn.

What if my swim shorts don't have a liner at all?

Some swim shorts are sold without liners for guys who prefer to choose their own base layer. In that case, a quick-drying sport brief made from synthetic material is a better option than cotton underwear — though a high-quality built-in liner means you don't have to think about it at all.

Do recycled swim shorts dry as fast as regular ones?

Yes, when engineered properly. High-quality recycled swim trunks that use tightly woven, fine yarns shed water just as fast — or faster — than conventional materials. Recycled content doesn't have to compromise drying performance.

How do I prevent chafing without wearing underwear under my swim trunks?

The key is a great liner and a great fabric. An ultra-fine micro-mesh liner prevents skin-on-skin friction, while a soft outer fabric avoids the rough, scratchy texture that causes irritation. A tailored fit also reduces excess material movement, which is a major contributor to chafing.