Constructed from a ribbed fabric this Active Extreme 1. 0 Base Layer acts in two ways to maintain comfort when you're active. Firstly the ribbed fabric increases surface area and helps trap air that is warmed by body heat when conditions are cold, whilst also radiating heat as you start to warm up. The close fit and ribbing also maximise sweat removal when you're active, drawing moisture from the skin allowing it to evaporate. This keeps you dry as you exercise but then avoids the chilling effect of that sweat build up as your workout comes to a close. Read more… Whether you're completing an intense cold weather bike ride or hitting the miles on a run the Active extreme base layer is there to keep you comfortable and warm.