The Castelli Thermoflex 2 Armwarmer. If you don’t need the extra wet weather protection of Nano Flex or if you’ve always been happy with traditional warmers you’ll find that Castelli’s Thermoflex warmers offer the softest most luxurious fabric combined with careful attention to construction details. Thermoflex fleece fabric is warm stretchy and soft. Single-piece construction with flat-lock seams. Embossed Castelli wordmark logos. Dual-sided silicone gripper elastic at top prevents sliding down. 8-20C 46-68F. Weight 61 g.