The US Open in New York is in its final stretch, but while the tennis has brought surprises — Roger Federer losing in the round of 16 to unseeded Australian John Millman — it feels like a lot of news around the tournament has been about fashion.

The latest stars to make headlines on that front are men's world number one Rafael Nadal and Maria Sharapova, both of whom wore a special Nike vest during practice sessions ahead of their next games (Sharapova crashed out in straight sets to Spain's Carla Suárez Navarro last night).

Now Nike has explained that the garment is actually a cooling vest, designed to reduce the stress on the body caused by high heat and humidity. Temperatures at Flushing Meadows have reached 95 degrees with humidity at nearly 50 percent, so Nike is doing everything it can to ensure its athletes stay cool and can perform at 100 percent.

According to Nike, although the vest has undergone extensive wear tests, this is the first time it has been worn for a tennis competition. The prototype being worn at the US Open was developed at the Nike Sport Research Lab after Nike researchers found that 75 percent of an athlete's energy becomes heat, increasing body temperature.

The resulting vest aims to combat that with four removable cooling packs that are placed to cover the maximum surface area across the front and back of the torso.

“Anything that can help with this heat is a benefit,” said Nadal. “We typically use wet towels to stay cool, but this vest gives me relief in all the places I need it. Every area of the vest was designed with players in mind.”

What do you think of Nadal and Sharapova’s cooling vest? Let us know in the comments.

In other news, Nike has made Colin Kaepernick a face of its latest “Just do it” campaign. Read more about that here and then check out the reactions here.

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