I purchased these to replace a pair of PI arm warmers I purchased about 10 years ago that were essentially fleece-lined lycra tubes. The anatomic shape of these warmers creates a very nice fit. Following the sizing chart provided in several websites including Pearl Izumi I purchased a small for my 12.5 inch arms. They are snug at the top but will not slide down and the length is very close to correct. On the road they are very warm but breathe quite well. The shape allows them to fit so well I don't notice I have them on except for the fact I'm warm. Overall excellent performance.