Updated October 2026
The short version
- No. In the water, skip everyday underwear. It's made for dry land, not the pool or the sea.
- If your trunks have no liner, or you want more support, wear a swim brief underneath. It's swimwear, so it belongs in the water.
- Save your boxer briefs for the trip there and back, and change at the beach.
It's one of the most-searched swimwear questions, and the answers online contradict each other. Here's the straight version.
Why everyday underwear and swimming don't mix
Everyday underwear is designed to be worn under clothes, on dry land. In the pool or sea it can sag, show through light-colored trunks and leave you sitting in a wet layer at lunch. Many pools also ask swimmers to wear proper swimwear only. It's not a disaster if you do it once. It's just not what underwear is for.
What to wear under swim trunks instead
Option 1: Nothing extra
If your trunks have a liner and you're comfortable, you don't need another layer.
Option 2: A swim brief underneath
This is the move a lot of men don't know about. A swim brief under board shorts gives you support and coverage made for the water. When you want to sunbathe or swim properly, the trunks come off and you're already dressed for it. A low-rise brief with a contoured pouch, like the Mandate Swim Brief, sits flat under shorts.
Option 3: Compression shorts made for swimming
Some men prefer a swim jammer or a swim-specific compression short as a base layer. Just make sure whatever you wear underneath is sold as swimwear.
Can you wear swim briefs as underwear?
You can on a beach day: wear your swim brief under shorts from the hotel to the sand and you're ready to swim. For everyday wear at the office, gym or on a flight, choose underwear made for that. Our Signature Boxer Brief is black, with a supportive contour and a flat waistband, in S–XL for $29.99.
Swimwear vs underwear: the quick comparison
| Swim brief | Boxer brief | |
|---|---|---|
| Made for | Pool, beach, sea | Daily wear under clothes |
| Wear it under trunks? | Yes, it's swimwear | Not for swimming |
| Wear it on a beach day? | Yes, under shorts until you swim | Only for the trip there and back |
| Mandate option | Mandate Swim Brief, $39.99 | Signature Boxer Brief, $29.99 |
Is wearing underwear under swim trunks normal?
Lots of men do it, mostly because they don't like the feel of trunks without a liner or want more support. The fix isn't more underwear. It's swimwear that does the job underneath. If you've been putting off briefs because they feel exposed, wearing one under trunks is an easy first step. Our first-timer's plan takes it from there.
The simple beach-day kit
- Swim brief on under your shorts.
- Boxer brief in your bag for the trip home.
- A second swim brief if you're out all day, so you can change into a dry one. That's what the Duo is for (two for $69.98). Going for a week? Get the Trio (three for $99.97).
Not sure which size? Check the size guide. Want care tips after the beach? Read How to Wash Swim Briefs. Without a discount code, orders over $99 ship free (over $60 in Israel).
Shop the brief
Mandate Swim Brief
$39.99
A low-rise brief with a contoured pouch and a flat logo waistband, in red or black, sizes S to L.
Shop the swim brief
Swim Brief Duo
$69.98 for 2
$10 less than two singles. Red and black, or two of one color, in one size.
Shop the Duo
Swim Brief Trio
$99.97 for 3
$20 less than three singles, and over $99, so it ships free without a discount code.
Shop the TrioShips from California. Without a discount code, orders over $99 ship free, and orders to Israel ship free over $60.
FAQ
Do you wear underwear under swim trunks?
Generally, no. Everyday underwear is designed for dry land. If you want more support or your trunks have no liner, wear a swim brief underneath instead.
Can you wear swim briefs under board shorts?
Yes. A swim brief under board shorts adds support and coverage made for the water, and you can take the shorts off to swim or sunbathe.
Can you wear swim briefs as underwear?
On a beach day, yes: wear them under shorts until you swim. For daily wear, choose underwear such as a boxer brief.
Is it weird to wear boxers under swim trunks?
It's common, but boxers aren't made for swimming. A swim brief or swim-specific base layer is the better choice.
What is the difference between underwear and swimwear?
Swimwear is made to be worn in pools and the sea; underwear is made to be worn under clothes. Many pools ask for proper swimwear only.