The castelli free 6 sock intended to keep your feet as cool as possible in hot conditions the castelli free 6 socks are especially light and breathable they39re made of meryl skinlife antimicrobial polyester fiber yarn so they evaporate moisture extremely well and noticeably reduce the accumulation of odors in the socks the mesh material that comprises the majority of the foot and ankle area is highly breathable and the reinforced arch and cuff keep the socks in place so they don39t