Technical sports socks have been developed for a number of sports, there are two main types: 'action' sport socks, and balance such as Pilates socks. Outdoor socks are quite popular, and usually good at maintaining body temperature when worn with trekking shoes, they're thicker in certain areas like heels, and the same is true for running socks, highly flexible in the middle in order to allow the foot to move freely and reinforced at the heel and forefoot. Compression socks have gained recent popularity among technical socks, especially in high muscular impact sports like crossfit and freeletics.