The Castelli Pro Issue SS Base Layer will keep you drier for longer. The Castelli Pro Issue Short Sleeve Base Layer was created after requests from Castelli pro riders looking for a highly wicking base layer for those in-between conditions where the Flanders is too warm and the Core Mesh is too cool.This isn\'t a thermal base layer, just something to move the moisture away from your body and help your race jersey perform. Castelli\'s 3D mesh fabric creates air space next to your skin, while the polyester capillary action moves sweat away.Castelli Pro Issue SS Base Layer FeaturesReduced seaming at shoulders for extra comfortWider collar to fit under aero jerseysFlat waist hem to lie flat in shortsWeight 48g (large)Castelli comfort range 15°-25°CCastelli Pro Issue SS Base Layer Materials100% polyester 3D mesh fabric