The swim cap is an essential piece of kit for Olympic swimmers, but why do they wear two?
The swimming finals are among the most anticipated events at the Olympic Games, and that promises to be no different at the 2024 Paris Games.
Frenchman Leon Marchand produced a stunning performance to win gold in the men's 400m individual medley final, before Team GB's Adam Peaty added a new chapter to his legend by taking silver in the men's 100m breaststroke final.
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Peaty missed out on goal by three hundredths of a second, highlighting the margins involved in swimming.
Such fine margins and the need to cut fractions of a second off their times is why swimmers wear swim caps.
Most competitors at the Paris Games - and indeed previous Olympics - have been wearing two caps to allow them to cut through the water with as little drag as possible.
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One reason for wearing one cap on top of another is to keep longer hair out of the swimmer's face.
But the other is that it helps to stabilise the swimmer's goggles by covering up the exposed straps, which in turn reduces drag in the water.
Less drag equals swimming with greater efficiency, which allows competitors to reach a higher speed and clock a faster race time.
Typically, the swimmer's goggles will sit on top of a latex cap, which is covered by a silicone cap.
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The friction between the latex and the silicone prevents the latter from slipping off, which stops the latex from wrinkling and tearing.
Dave Salo, an assistant coach for the 2012 US Olympic Women’s Team, explained to Yahoo!: "The outer silicone cap better maintains the shape and does not wrinkle as much, thereby causing less drag."
While caps rarely fall off, Dana Volmer won goal in the 100 butterfly at the 2012 London Games despite one of her caps coming off.
Alex Brotherton