The castelli thermoflex arm warmer is a must for the colder weather conditions its super comfortable and stretchable design makes it ideal for use with your short sleeve jersey in the winter where you don39t want to brave any bare skin showing made from the unique thermoflex fabric the castelli thermoflex warmer provides a super comfortable fit thanks to its stretchable and soft construction with a microfiber gripper elastic at the top you can also be sure that the arm warmers