TL;DR: Stop wearing underwear under your swim trunks. Seriously. Boxers and briefs under swimwear cause chafing, trap water, and make everything take twice as long to dry. The real solution is finding comfortable swim shorts with a high-quality built-in liner that provides support, dries fast, and eliminates the need for anything underneath. Your best bet is an ultra-fine micro-mesh liner — like the one in Blauw's comfortable swim shorts — that offers breathable support without the slow-drying sponge effect of compression liners.
It's one of those questions most guys Google privately but never ask out loud: What am I supposed to wear under my swim trunks?
And honestly, it's a fair question. The first time you try on a pair of swim shorts and feel that flimsy mesh net dangling inside, your instinct is to throw on a pair of boxer briefs for backup. It feels like the safe move.
But here's the thing: wearing underwear under your swimwear is almost always the wrong call. It creates more problems than it solves, and the real fix isn't adding another layer. It's choosing the right swim shorts in the first place.
Why Most Guys Wear Underwear Under Swim Trunks
Let's start with the "why," because it's completely understandable.
Most men reach for underwear under their swim shorts or trunks for one of these 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.
These are all legitimate concerns. But the solution isn't layering regular underwear underneath. The solution is better swim shorts.
Why You Should Never Wear Underwear Under Swim Shorts
Wearing boxers, briefs, or boxer briefs under your sustainable swim trunks creates a chain reaction of discomfort that gets worse as the day goes on.
1. Cotton Underwear Absorbs and Holds Water
Cotton is designed to absorb moisture. That's great for a normal day. It's terrible in the water. Cotton underwear soaks up water like a sponge and holds it for hours. Even if your swim shorts dry quickly, the layer underneath stays damp, heavy, and clingy against your skin.
The result? That soggy, uncomfortable feeling that makes you want to change the second you leave the beach.
2. It Creates Friction and Chafing
Wet fabric layers rubbing against each other — and against your skin — is a recipe for chafing. The seams on regular underwear aren't designed for wet, sandy conditions. Add movement (walking, sitting, swimming) and you've got irritation that can ruin an entire afternoon.
3. It Slows Down Drying Time Dramatically
One of the most important features of modern comfortable swim shorts is quick-drying performance. But even the fastest-drying swimwear for men can't overcome a soaking-wet cotton layer trapped underneath. You effectively cancel out the quick-dry 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. Wearing 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 unnecessary bulk around the waistband and thighs, which kills the clean silhouette of a well-tailored pair of swim shorts. If you've invested in a modern, streamlined fit, underwear underneath literally undoes the look.
The Real Answer: Find Swim Shorts With a Great Liner
Instead of layering underwear underneath, the move is simple: 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 — all without the downsides of an extra layer.
But not all liners are created equal. Here's the breakdown.
The Three Types of Swim Short Liners
1. Traditional Mesh Netting
This is the scratchy, loosely woven net you'll find in most budget swimwear. It technically provides a barrier, but offers minimal support, can irritate the skin, and feels cheap against the body. It's the reason so many guys started wearing underwear underneath in the first place.
Verdict: Better than nothing, but barely.
2. Compression Liners
Compression liners (like built-in bike shorts) have become popular in recent years. They offer excellent support and eliminate chafing concerns. However, they come with a major tradeoff: they absorb significant amounts of water and take a very long time to dry.
If you're looking for all-day swim shorts that transition from water to lunch to evening plans, compression liners work against you. You'll be sitting in a damp, heavy liner for hours.
Verdict: Great support, terrible drying time. Not ideal for all-day wear.
3. 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 (So You Never Think About Underwear Again)
If you choose the right pair of comfortable swim trunks, the "what do I wear underneath?" question disappears entirely. Here's your checklist:
Ultra-Fine Micro-Mesh Liner
As covered above, this is non-negotiable for all-day wear. It should feel light, breathable, and almost invisible — providing support without adding bulk or trapping moisture.
Quick-Drying Outer Fabric
The outer fabric should shed water rapidly. Look for a tight weave with fine yarns — this prevents water from lingering between fibers and dramatically speeds up drying time. A fabric that dries in minutes means you're never sitting around in wet shorts.
Soft-Touch Material
If the fabric feels stiff, scratchy, or plasticky when dry, it's going to feel worse when wet and covered in sand. The most comfortable swimwear for men uses ultra-fine yarns that create a buttery-soft hand feel from day one — no break-in period required.
Tailored Fit
A modern, tailored cut (around a 5-inch inseam) sits comfortably without excess fabric bunching up. Less excess material means less friction, less water retention, and a cleaner look that works beyond the beach.
Salt Water and Chlorine Resistance
If you're swimming regularly — in the ocean or the pool — your shorts need to hold up. Quality recycled swim shorts are engineered to resist degradation from salt water and chlorine, keeping the fabric soft and the color true over time.
Our Top Recommendations
1. Blauw Swim Shorts
Blauw was built for exactly this use case: swim shorts you never want to take off. The OceanKnit™ fabric — developed from regenerated ocean plastic in partnership with SEAQUAL — is buttery soft, ultra quick-drying, and structured enough to look sharp all day. The ultra-fine micro-mesh liner provides breathable, chafe-free support without the slow drying times of compression liners.
With a clean 5-inch inseam, basic refined colors, a signature teal drawstring, and salt water and chlorine resistance, Blauw sustainable swim shorts are designed so the underwear question never crosses your mind.
Best for: All-day comfort, quick drying, sustainable swimwear for men, soft fabric, and a clean silhouette that transitions from the water to dinner.
2. Patagonia Baggies (5-Inch)
A solid, well-known option with quick-drying fabric and a simple design. They use recycled nylon and offer a relaxed fit. The liner is functional, though not quite as refined as micro-mesh options. A good choice if you prioritize brand familiarity and a slightly looser cut.
3. Outerknown Nomadic Volley Shorts
Made with recycled materials and featuring a comfortable elastic waist, these offer a clean, surf-inspired aesthetic. Good for casual beach days, though the fabric doesn't dry quite as fast as tighter-weave options.
The Bottom Line
Stop wearing underwear under your swim trunks. It's not solving the problem — it's making it worse.
The actual fix is investing in comfortable swim shorts with an ultra-fine micro-mesh liner, quick-drying fabric, and a tailored fit that works for your entire day. When those three things come together, 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 summer 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 any of the downsides of compression or traditional mesh.
- Quick-drying fabric matters. A tight weave with fine yarns ensures your shorts shed water in minutes, not hours.
- Invest in all-day swim shorts. The right pair eliminates the need for underwear entirely — look for soft fabric, a tailored fit, and premium construction.
- Sustainability doesn't mean sacrifice. Recycled swim trunks like Blauw's OceanKnit™ shorts prove that ocean-first materials can deliver best-in-class comfort and performance.
Frequently Asked Questions (FAQ)
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 they absorb and retain water, leaving you with a heavy, damp layer that takes hours to fully dry. A built-in ultra-fine micro-mesh liner gives you support without the slow-drying downside.
Why do swim shorts even have liners?
Liners serve as a built-in undergarment that provides support, reduces chafing, and adds a layer of 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 this case, a quick-drying sport brief made from synthetic material is a better option than cotton underwear. But ideally, choose swimwear for men with a high-quality built-in liner so you don't need to think about it.
Do recycled swim shorts dry as fast as regular ones?
Yes — when engineered properly. High-quality recycled swim trunks, like those made with Blauw's OceanKnit™ fabric, use tightly woven ultra-fine yarns that shed water just as fast (or faster) than conventional materials. The recycled content doesn't 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 (like OceanKnit™) avoids the rough, scratchy texture that causes irritation. A tailored fit also reduces excess material movement, which is a major chafing contributor.
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