They don't need to be cycling specific. They should be a wicking material. For warm/hot weather, a thin synthetic (coolmax is one trade name for this fabric) works really well- I prefer the really short ones that don't show at all, but i do have some cycling ones that are just above the ankle. For cooler or wet weather, wool is the best. It still wicks, but it has some insulating properties that generally do not diminish when wet. Cotton socks are a non-starter. They just get sweaty and smelly.