Whether you're racing or training in changeable conditions, it can be difficult to decide whether to go out in a long sleeve or short sleeve jersey. The Castelli Nano Flex 3G Arm Warmers gives you the best of both worlds. For cooler and damp conditions, slip them on to provide extra warmth and wet weather protection from the water repellent finish on the fabric. Should the clouds break, and the sun shows up, they're easy to take off and stow in a back pocket.