Yes, it’s comfortable in all sleep positions. The head strap is made from organic cotton, and it is super soft on the head, you won’t even notice it’s there. For side sleepers and belly sleepers: The foam is super soft so even if you lie on your side or on your belly, you will find our No-Rays’ Mask molding to your face and not causing any irritation. Please note that the concept of this mask might be new to you if you’re not used to a mask that provides a near-perfect experience (complete blackout without even touching your eyes!) so it might take a couple of days to adjust to this luxury (Or maybe not even one hour…)