When I received this mask I tried it on in the daytime in a sun filled room and it blocked all but just a pinhole's worth of light. If I tighten the strap I can get rid of that last tiny bit of light but it's less comfortable to wear all night that way. It's fairly thick and on the rare occasion if the room I'm sleeping in gets a little warm I'll wake up with a little dampness around my eyes but with central A/C most nights this is not an issue. The strap holds very securely even though I tend to move a little in my sleep.

Sleeping on my side, back, or on my stomach it has only come off 2 or 3 times in several months of use. The fabric is high quality and very soft, inside and out. Definitely has helped improve the quality and quantity of my sleep.