It's tough to make arm warmers warmer. If we know we'll be riding in conditions where a pair of arm warmers won't keep us sufficiently warm, we tend to choose a thermal jacket. But, what if the day turns out to be intermittently cold and wet' Well, the Castelli Nanoflex Arm Warmers are designed for days that deliver everything from cold and wet to sunny and dry. Nanoflex is a proprietary Castelli fabric. The mill begins with Castelli's super warm and ultra stretchy Thermoflex fabric, used in many of its winter pieces, and then coats the outside with tiny nanofilaments of silicone fiber. These fibers create a near waterproof barrier to moisture, and raindrops run off the fabric without soaking through. Despite its water resistant finish, Nanoflex fabric remains highly breathable, keeping you comfortable in almost any conditions. Silicone arm grippers keep the arm warmers in place on the hardest rides, and reflective logos are printed at the elbow and lower arm to increase your visibility to motorists in poor light conditions. The Castelli Nanoflex Arm Warmers are available in four sizes from Small to X Large and in the colors Black, Red, and White. Please note that Castelli recommends using these warmers at temperatures ranging between 50 and 60 degrees Fahrenheit.