The Exped VBL Socks are lightweight liners for extremely cold undertakings They are a must for Himalayan mountaineering and Arctic or winter adventures. These are vapor impermeable and are worn over thin or under heavy socks. This prevents shoe insulation from getting damp from sweat and helps to keep feet warmer. The seam at the heel and toes is designed to reduce rubbing and blisters, the VBL Socks are also very comfortable to wear. Keeps the shoe insulation dry Vapour barrier keeps feet warm Heel and toe seam designed to reduce friction Weight S: 35 g M: 40 g L: 50 g