This is a Merino base layer, a classic item that has been the foundation of Rapha's development. I own several different colors and have used them a few times. The size is M, but because it's knit and very stretchy, it's suitable for those who usually wear M-L size in Rapha, or L-XL in the Pro Team line. Thanks to the properties of merino wool, it feels good against the skin, is warm, and doesn't get cold from sweat. Perfect for long winter rides. I will ship immediately.