Some people can sleep through a day at the beach or even with a rattling train or jackhammers working nearby. Others need to block out every ray of light and sound in the vicinity. For those folks - thankfully - there are sleep masks out there. A great sleep mask should block out as much light as possible without feeling as if you’re wearing a dive mask and snorkel to bed. A mask should provide for easy movements of the eye - especially during REM sleep - but also stay in place during the night. Here are four sleep masks we recommend.