Thermoflex 2 Arm WarmersThe Castelli Thermoflex 2 Arm Warmers are made of luxurious, stretchy, soft fleecy fabric. The stretchiness allows a more aerodynamic fit. They will keep your arms warm and comfortable throughout your winter rides. If you overheat, simply roll them into a neat bundle and pop them into the back of your jersey pocket. The silicon gripper ensures they do not slide down the arm. Check the Sizing Chart Features Thermoflex fleece fabric is warm, stretchy