The swimsuit liner is your underwear.

The liner is there so you don’t have to – and shouldn’t – wear underwear underneath.

It’s sewn in for a reason: it’s a built-in layer for hygiene and modesty. That mesh or fabric panel covers your crotch so the suit can be worn directly against your skin without needing separate underwear (which would get soaked and bunch up in the water anyway). The liner also helps smooth out lines.

Some people rip them out thinking they’re unnecessary or uncomfortable. You can, but then you’re wearing a swimsuit that’s one layer thinner, and you’ll either go commando or deal with wet underwear all day. If the liner bothers you, look for suits with removable cups or a different cut – don’t just cut the liner out as a first step.

It’s not a design flaw. It’s a built-in pair of underwear that’s designed to get wet.