Turns out that while the lower swim cap fits on a swimmer's head better, it can wrinkle and create drag, which could very well create the split-second difference between getting a medal and getting nothing. To combat this, many swimmers layer on a second cap made of a silicon material and often wear their goggles between the two caps as well, according to the report. Of course, there may be other factors like comfort, for example, and there are certainly some swimmers who wear only one cap.
But then again, it's probably nice to have two caps to toss into the audience when you win a gold medal, right? Well, that is if they can make the throw.