Swim Trunks vs. Board Shorts: What's the Difference and Which Should You Buy?

TL;DR: Swim trunks and board shorts look similar on a hanger, but they're built for very different days. Board shorts are longer (typically 8–11 inches), use a flat velcro-and-lace waistband, rarely include a liner, and are optimized for surfing. Swim trunks sit shorter (5–7 inches), feature an elastic waistband, usually include a built-in liner, and are designed to work both in and out of the water. If you surf daily, board shorts make sense. If you want one pair that handles swimming, walking, lunching, and everything in between, quick-dry swim trunks are the more versatile pick.

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Most guys use "swim trunks" and "board shorts" interchangeably. And honestly, plenty of brands blur the line on purpose — it sells more product.

But the two are genuinely different garments, designed for different activities, with different construction. Choosing the wrong one doesn't ruin your vacation, but it can leave you dealing with soggy fabric at lunch, an awkward silhouette at dinner, or a waistband that won't stay put in the waves.

Here's a direct, category-by-category breakdown so you can buy the right pair for how you actually spend your summer.

What Are Board Shorts?

Board shorts were born in surf culture. They were designed specifically to be worn on a surfboard — and everything about them reflects that origin.

They sit below the knee (usually an 8- to 11-inch inseam, sometimes longer), use a rigid flat waistband with a velcro fly and lace tie, and almost never include an interior liner. The longer length protects your thighs from wax rash on the board, and the flat waistband avoids the bulk of elastic when you're lying prone and paddling.

If you've ever watched a surf competition, those are board shorts.

What Are Swim Trunks?

Swim trunks are the broader, more versatile category of men's swimwear. They're built for general water use — the pool, the ocean, a lake — and increasingly for everything you do around the water, too.

They typically feature a shorter inseam (5–7 inches), an elastic or elastic-and-drawstring waistband, and a built-in liner for support. The fabric tends to be lighter and finer than board-short material, which helps them dry faster after a swim and look more like a casual short than a piece of athletic equipment.

Length and Inseam

This is the most visible difference between the two.

Board shorts: 8–11+ inches. They were designed to hit at or below the knee. The extra length serves a functional purpose on a surfboard (thigh protection), but off the board, it can look bulky and dated — closer to the mid-2000s baggy aesthetic than anything you'd see in a modern summer wardrobe.

Swim trunks: 5–7 inches. A modern swim trunk sits mid-thigh, creating a cleaner, more proportional silhouette. A 5-inch inseam tends to be the sweet spot: short enough to look sharp, long enough to feel comfortable sitting, walking, and swimming.

The takeaway: If you're choosing based on how they look outside the water, shorter swim trunks win easily. Board shorts are purpose-built for the board, not the boardwalk.

Waistband

Board shorts: Flat, rigid waistband with a velcro closure and internal lace tie. This keeps the shorts locked in place when you're getting tossed by waves or duck-diving under whitewater. It's functional for surfing, but it's bulkier under a t-shirt and doesn't adjust as easily for casual comfort.

Swim trunks: Elastic waistband, usually with an external drawstring. This is simpler, more forgiving, and far more comfortable for extended wear. A good elastic waistband sits flat, moves with your body, and doesn't dig in after a big lunch.

The takeaway: For surfing specifically, the board-short waistband is more secure. For literally every other activity — swimming, walking, eating, lounging — an elastic drawstring waistband is more comfortable and more practical.

Liner

Board shorts: Almost never include one. Surfers generally prefer to wear their own base layer (rash guard shorts or compression briefs) underneath, or nothing at all. This gives them control over fit and avoids the potential for a liner to bunch or chafe during long paddle sessions.

Swim trunks: Most include a built-in liner. This is where quality really varies. Cheap mesh liners can feel scratchy and trap water. Heavy compression liners dry slowly and feel like wearing a second pair of shorts. The best option is an ultra-fine micro-mesh liner — lightweight, breathable, and fast-draining — which provides support without the drawbacks. If you want to understand the full range of what to wear under swim trunks, it comes down to liner quality.

The takeaway: If you're surfing for hours, you might prefer the freedom to choose your own underlayer. For everything else, a good built-in liner simplifies your life and makes the shorts ready to go straight out of the drawer.

Fabric and Drying Speed

Board shorts: Traditionally made from heavier-weight polyester or polyester-spandex blends. The fabric is thicker and more abrasion-resistant to hold up against surfboard decks and wax. The trade-off? Heavier fabric means slower drying times. You'll notice this the moment you try to wear board shorts to lunch after a session — they can stay damp for a surprisingly long time.

Swim trunks: Built from lighter-weight fabrics engineered for quick drying. The best swim trunks use a tighter weave with finer yarns, which sheds water rapidly instead of trapping it between fibers. Blauw's OceanKnit™ fabric, for example, is woven from ultra-fine recycled yarn and dries in approximately 7 minutes — which means you can step out of the ocean and sit down at a restaurant without leaving a puddle on the chair.

The takeaway: Drying speed is one of the biggest practical differences between the two. If your day involves more than just surfing — which, for most men, it does — a quick-dry swim trunk is dramatically more practical.

Surfing Performance

This is the one category where board shorts have a clear, purpose-built edge.

The longer inseam prevents wax rash on your inner thighs. The flat waistband eliminates bulk when you're paddling. The lack of a liner means nothing bunches or shifts under a wetsuit. And the heavier fabric can take the abrasion of sliding on and off a board dozens of times in a session.

If you surf regularly — not "I tried it once in Bali" but actually paddle out multiple times a week — board shorts are designed for you, and they do that job well.

That said, plenty of casual surfers wear swim trunks in the water without any issue. A pair with a 5- or 7-inch inseam and a snug drawstring waistband works perfectly fine for a mellow surf. You'll only notice the difference if you're in the water for hours at a time.

Casual Versatility

This is where swim trunks pull ahead significantly.

Board shorts look like what they are: surf gear. The knee-length cut, technical waistband, and often bold graphic prints signal "I just came from the beach." That's fine at a surf shack, less fine at a waterfront restaurant or a rooftop bar.

Swim trunks — especially modern, tailored versions — blur the line between swimwear and everyday shorts. A well-fitted pair with a clean design, muted color palette, and refined fabric can easily pass as casual shorts. You can walk through town, sit down for coffee, go for a swim, and transition straight to dinner without anyone clocking that you're wearing swimwear.

The takeaway: If you want one pair of shorts that handles your entire day — not just the water portion — swim trunks are the clear winner.

So, Which Should You Buy?

Here's the honest answer:

Buy board shorts if you surf frequently, you want thigh protection on the board, and you don't mind changing into something else afterward.

Buy swim trunks if you want a single pair of shorts that works in the water, out of the water, and everywhere in between. For the vast majority of guys — the ones who swim, travel, walk, eat, and occasionally jump off a dock — a pair of well-made quick-dry swim trunks will serve you better, more often, and in more situations than board shorts ever will.

The real question isn't "which is better?" It's "how do you actually spend your summer?" Answer that honestly, and the choice makes itself.

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FAQ

Can you surf in swim trunks?
Yes. For casual and moderate surf sessions, a well-fitted pair of swim trunks works fine. You may experience some thigh friction on a waxed board during longer sessions, which is where board shorts' extra length helps. But for most recreational surfers, swim trunks are perfectly adequate.

Why are board shorts so long?
The extra length was originally designed to protect surfers' thighs from chafing against surfboard wax. Over time, the longer cut became a style trend in its own right, but the functional origin is purely about thigh protection on the board.

Do board shorts dry faster than swim trunks?
Generally, no. Board shorts tend to use heavier, more abrasion-resistant fabric that holds onto water longer. Swim trunks — especially those with lightweight, tightly woven fabric — are engineered to shed water quickly and dry much faster.

Can you wear board shorts as regular shorts?
You can, but they don't look as polished as tailored swim trunks. The longer cut, flat velcro waistband, and typically louder designs make them read as sportswear. Modern swim trunks with a 5-inch inseam and clean styling are far easier to pass off as everyday summer shorts.

Do swim trunks always have liners?
Not always, but most do. The quality of that liner matters enormously. Cheap mesh liners chafe and trap water; heavy compression liners dry slowly. The best swim trunks use an ultra-fine micro-mesh liner that provides support, drains water instantly, and stays comfortable for hours.