In a sport where every millisecond counts, you probably don’t want to be burdened with a single ounce of unnecessary apparel. That’s why swimmers opt for Speedos, not cargo pants, and tend to shave their body hair to reduce drag.

But that minimalism usually has one exception: Many athletes opt for two swim caps. Why?

According to Quartz, it’s because each cap meets a different need. An inner cap made of latex forms snugly with the head but can wrinkle when exposed to water, creating resistance. To compensate, athletes add a silicone cap as an outer protective layer. Combined, the caps also secure goggle straps to the head.

So why not just wear silicone by itself? Because it tends to slip off when fitted directly onto the scalp. And while swimmers are usually meticulous about shaving their bodies, buzzing their hair probably wouldn’t be preferable: A stubble-ridden dome is unlikely to reduce drag more than a sleek silicone membrane.

Such a practice would have also deprived fans of celebrations like Sun Yang’s: The Chinese gold medalist tried to celebrate his win in Rio by triumphantly tossing his cap into the crowd. It didn't go as planned. You can watch the reasonably embarrassing action below.

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