I am currently investigating if arm sleeves will help my hands from getting as cold on 30-40 degree days. I ran with short sleeves, no gloves, shorts and my new Nike Arm Warmers, and found that my hands did get cold, but not as much as I expected. The temps were in the mid-40’s and it was windy… about 15mph. I got size = x-small and found that they are snug, but not bone-crushingly tight. They held up on my upper arms fine. They are quite thin, so I guess for cooler temps, I’d want something fleece-lined.