And as Xhaka suits up to represent his home country of Switzerland in its World Cup opener Sunday against mighty Brazil, he’ll need all the rest he can get.

To do that, Xhaka has become a sleep science guinea pig of sorts.

Under Armour, the US-based sporting apparel company that sponsors him, has probed and prodded Xhaka to find out what makes him tick when he’s not on the field.

But they’re also trying some fishy-sounding next-gen tech, like special sleepwear and sheets with ceramic woven into the fabric.

The material is supposed to stimulate blood flow and keep sleepers warmer—it supposedly absorbs heat from the body and re-emits it back as far-infrared radiation, and some small studies have shown that ceramic fabrics can help with arthritis and menstrual pain.

But the connection with better sleep hasn't been proven—and at $200 a set, it's an investment fairly limited to pro athletes.

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