KEVIN B.wrote a review of Castelli Nano Flex Arm Warmers on August 16, 2013
Familiarity: I've put it through the wringer
I use Castelli arm warmers for my early morning rides where the temps are 60F or below. They're useful down to 50F w/o sun and perhaps 45F w/warming sunshine. I overlap the tops on the sleeves of my Gore WS short-sleeve base. It's a good combination between 50F and 60F. The arm warmers store well in a back pocket as the day warms into the mid-60s. I use the white model when riding pre-dawn for visibility. The black warmers absorb radiant heat during the day. The grippy tops stay up well thus far. I have 37" arms; the XL fits just right. I've used these for two, perhaps three years. An improvement would be to add reflective materials as is typical on Gore products.