For surfing, windsurfing, kitesurfing and similar sports, bootees are typically worn where the weather is so cold that the surfer would lose some degree of functionality in the feet. The bootee should not restrict the ability of a surfer to grip the board with the toes in the desired manner. Split-toe bootees allow for some improvement in this functionality. Reef walkers are small bootees that are only as high as the ankle and generally only 2 to 3.5mm thick. They are designed to allow surfers to get out to waves that break at coral reefs or at rocky beaches.