Spain are wearing special vests filled with frozen gel to keep cool during training in the hot temperatures at the North American World Cup.
The Spanish football federation said on Saturday that the 2010 winners and 2026 favourites were one of 14 sides at the World Cup using the new technology, which has been developed by German sportswear firm Adidas.
A federation statement said the garments can reduce core body temperature by up to 0.5 degrees Celsius and skin temperature by up to 13 degrees.
The move puts Spain "at the forefront of technology to ensure players compete in the best possible condition."
European champions Spain open their campaign against debutants Cape Verde on Monday in Atlanta. The stadium there has a roof so the players and fans will be shielded from immense heat, but Spain's training ground in Tennessee is open.
Top wingers Lamine Yamal and Nico Williams returned to full training earlier this week after minor injuries.
