On the surface, Castelli Nanoflex Arm Warmers seem like most medium-weight arm warmers but high-tech, Nanoflex fabric and construction details take them to the next level. Castelli uses Nanoflex fabric which is similar to Thermoflex in terms of sharing a soft, brushed interior for comfort and warmth. Nanoflex has a silicone impregnated surface which provides better water repellency and wind resistance clearly a notch above other arm warmers. They are not fully waterproof, but will keep you comfortable in all conditions much better than most other arm warmers.
Overall, the Nanoflex arm warmers have a very protective feel. They work in a wide 45-65ºF temperature range. A detail we like very much is silicone grippers on both the inside and outside to keep the both the arm warmers and the jersey sleeve in place. They are designed to fit tightly. The Large size will fit to about a 14 or 15" upper arm so they might be a little tight for those with more of a linebacker's build.