These have been great for winter mornings in the high 40s, and I leave them on until the temps climb into the mid-50s. When they're on, I forget they're there. When I remove them, they easily stow away in my jersey pocket.
These are great arm warmers for chilly to very cold rides. Keep in mind that only one of the two arm warmers comes marked with the Castelli logo shown in the image above, the other arm warmer is just plain black.