Castelli Pro Issue Short Sleeve the best in base layers Castelli's Pro Issue is perfect for those in- between conditions where the Flanders is too warm and the Core Mesh is too cool, like Spain in February or Belgium in April. You're not looking for warmth from your base layer, just something to move the moisture away from your body and help your race jersey perform. Castelli's 3D mesh fabric creates dead air space next to your skin, while the polyester capillary action moves sweat away. Features 100% Polyester 3D mesh fabrick with reduced seams provides extra comfort Wide collar fit fits well under aero jerseys Flat waist hem lets Pro Issue lie flat in short | Castelli Pro Issue Short Sleeve Men's Size Medium in White