I have never worn arm warmers and regularly just ride in summer kit until the temps fall below ~40 degrees F. so I was a bit disappointed that these arm warmers only seemed to make my arms feel colder as they accumulate enough sweat to cause evaporative cooling. If I take them off, my arms actually feel about the same. So I cant say I am any more comfortable with them on on a day when the temps are in the mid 30s to mid 40s. However, under a wind breaker or winter riding coat, they do enhance warmth so they have a net utility (under 30 degrees). as for fitment, I measure for what should be a medium size but i would say that the elastic around the biceps are pretty tight. i would probably get a size larger if I were to buy again
Coming off hot summer want wanting some options for fall, decided to get a pair. i'm about 15" in the upper arm but automatically ordered a large based on measurements I must have taken wrong and some fits I had done in a store last year. Too small. Swapped for X-large. They barely fit and I guess that's the top of the sizing range, so I'd say order a touch bigger than the sizing would indicate. I tried them on other day as temps fell to 68-72 and I was feeling chilly. They helped and were mostly adequate for the slight drop in temps but not much more. They felt chilly in the wind and shade and I don't think I would want to wear them in much cooler weather.
these are good arm warmers... great for those chilly morning commutes in early spring/ fall or as a layer during the winter. on week end rides they are nice and easy to store away in the jerseys pocket as the day warms up. i really do not think i could ride in Oregon with out arm warmers and these are a fair price and a good quality.
For some reason unclear to me now I thought these were men's sized, but they're unisex, so being a guy that wear's medium men's size I needed to return that pair and get a large unisex size. I have always been happy with Pearl Izumi arm and knee warmers, and these look like they will be great once I get a good fitting pair.