I’d say that length is the primary difference of board shorts and swimming trunks. The swimming trunks, however, may be more fitted than the board shorts. I’ve seen other subtle differences between the two as well.
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Primary Features
Both board shorts and swimming trunks come in a variety of styles and colors. For instance, you can find plain black or navy swim trunks. Alternatively, you can choose board shorts with stripes, gradients or seashells and other sea creatures printed on them.
Some may have front or back pockets in them for holding your keys or wallet. If you prefer less fabric bulk, however, you might find some shorts and trunks made with no pockets.
Whether you wear board shorts or swimming trunks, make sure you choose a pair that feels comfortable to you when you try them on. You don’t want pants that are too tight or too loose – both cases uncomfortable to wear in the heat.
The Design
Board shorts typically have as wide of a waistband as possible without them falling to your ankles. They usually fit looser, especially in the thigh and buttocks area. Some may have drawstrings to hold them onto your waste, but others may have elastic bands.
Swimming trunks, on the other hand, typically have a narrower waistband and have a tighter fit but are still loose enough to maneuver. Swimmers, by the way, usually prefer less fabric when propelling underwater because it reduces the chance that water shorts will become bunched up during movement.
Liner or No Liner
Wearing liners often provide extra support in the private region. Mesh liners provide climate control for the personal areas of the body that otherwise might sweat too much. Liners also prevent chafing sometimes caused by the outer material rubbing against the skin.
Some people may wear board shorts in the water with liners, compression shorts or other undergarments. However, board shorts typically don’t have a built-in mesh liner, but swimming trunks traditionally do.
Experienced surfers oftentimes prefer wearing board shorts with no underwear or liner. However, some of them might like the comfort of the extra support a liner can provide. Built-in stretch liners may also provide benefit to some users, but I’d prefer to have them as two separate units instead of attached to one another—too many bad experiences with untangling the inner layer before dressing.
The Material
Both swimming trunks and board shorts have lightweight materials. That’s because they’re meant for maximum maneuverability in the water. Swimming trunks might feel bulkier because of the mesh or cotton lining inside them. However, the primary, outer layer of board shorts may have a firmer fabric that provides more resilience than swimming trunks because surfers might need the extra strength when riding waves.
On the other hand, swimming trunks with a thermal lining may keep you warm if you can’t wait to enter the water even if the outside temperature reads cooler than normal. Alternatively, you can find a pair of lightweight trunks that will allow your skin to breathe if you plan on swimming in hot weather.
The Fabric
Swimming trunks usually contain polyester or nylon, usually with a mesh lining but sometimes a solid cotton one. Some trunks made for the water have elastane for the stretch waist, or they might offer spandex mixed in with the base material. The lining inside the pockets may contain either cotton or polyester.
Board shorts may also come in polyester or nylon, and both these and some swimming trunks have been made from recycled fishnet materials. I didn’t even know this, but even plastic bottles have turned into new shorts made for the water.
The Good Trade backs up the use of recycled materials in nine different brands:
“For the best swimming trunks, these brands are using recycled materials like plastic bottles, ocean waste, and regenerated nylon.”
The Length
Surfers usually need the range of motion that also covers them like longer shorts would. That’s why board shorts usually come down closer to the knee than swimming trunks. Swimming trunks usually extend to no longer than about mid-thigh. Board shorts probably measure up to about 22 inches. Swimming trunks may only extend about 4-7 inches inseam or maybe 16-18 inches from the waist to the knee.
Coverage
If you’re looking for something that will last through lots of activity and provides more coverage, go with board shorts. If you want something lightweight and less constricting when doing laps in the water, choose swim trunks.
Either way, both swimming trunks and board shorts don’t usually have an underwear fly, which also adds to water coverage. However, they might have either elastic or a zipper fly and a button closure to make sure nothing that shouldn’t “peep out” stays concealed.
Real-Life Usage
Board shorts provide more coverage than swim trunks do when surfing. However, some vacationers use them when you don’t have to worry about accidentally exposing yourself. However, it doesn’t mean that swimmers can’t wear trunks with longer legs. They can, but it can prevent them from moving their legs as easily as they’d like.
I don’t see a problem with using board shorts as swimwear, by the way. However, surfers may not always successfully wear swim trunks while riding waves unless they have compression shorts made from stretchy material underneath them that clings to the body.