Some days, all we need is a thin, streamlined pair of socks with just a little bit of extra warmth, but on the really frigid and snowy days, we want all the insulated protection we can stuff into our favorite pair of cycling shoes. On those days, pull on a pair of Castelli Fatto 12 Socks and bask in cozy, insulated warmth. Made from a mix of soft PrimaLoft and polypropylene yarns with terry cloth to boost those fabrics' already insulative properties, the Fattos will be your best friend through winter training rides, bone-chilling commutes, and overly air-conditioned office environments.