I like these for slightly cooler days, the material is a bit heavy I think for really hot 90 degree plus days. But the material and quality otherwise is excellent. I have many Castelli products and never disappointed once you get size right
These were purchased to eliminate the need to use sun screen on longer rides.
I am 5'11 with a small frame and average length arms for my height. The large sleeves are the proper length and have a loose fit. They have gripper elastic to help keep them up via friction with the jersey sleeves. So far it is working but time will tell whether the size is a problem or not.
I don't notice them making my arms feel warm while riding but do notice the heat when stopped. One thing you can do is wet them and then you have cooling unless it is really humid.
I've had my arms burnt badly on several IM triathlons since the sunblock eventually sweated off, either on the bike or run. These solved the problem. They weren't buky or bothersome and transitioned to my jersey. I didn't notice them, and I didn't get burnt (in South America during their summer).
Of course they were-they're Castelli....still, they really weren't as comfortable as I hoped and I tried multiple sizes. I ended up going with Pearl Izumi-cheaper, more comfortable and less visible logos. I love Castelli and own lots of gear, but these didn't do it for me.
Though more expensive than competitors, the material is a better quality. It is not hot even in direct sunlight and over 90 degrees. Much better than a thick layer of suntan lotion that may not work and allow direct sun making it feel hotter.
having just survived stage 1 melanoma surgery these are now my go to product for sun protection. no more slogging on icky sunscreen multiple times during a fun ride. yes they are very lightweight. they wick moisture away very adequately. got the white ones for extra coolness but they do show the dirt more than the black ones. i use these sleeves for both long distance riding and hours of tennis. i am 5'712 128 lbs and the medium fits very nice. i was concerned about the length for my long arms and these work perfectly. they are a bit pricey but worth every penny to prevent a return of any cancer.
These skins will be used to shield the sun on mild days when heavier warmers are not needed. Of course Castelli quality and fit are a bonus. They fit in a jersey pocket without bulk.