I wore these for a mountain run today, which started out chilly and turned sunny. The sleeves kept the initial chill away but, as the morning warmed up and I started to sweat, the cooling action kicked in. I felt very comfortable and did not feel confined or overly hot. I am 4’11” and petite. My bicep is 10” and my wrist is 5 1/2”. I ordered the XS/S and they fit perfectly! The sleeves stayed in place with no bunching up. They did not slip down my arms and there was no chafing under my arms. These will be an essential piece of my trailwear for the summer!