While they look otherworldly, sheet masks are pretty simple: paper or fabric drenched in serums and essences that give your skin a boost in just 10-15 minutes. They're portable, effective, and facilitate incredible selfies. They come in the form of a thin mask with holes for eyes, nose, and lips. Place one over your face before bed, put on some relaxing music, and create a quick, rejuvenating spa-like experience right at home. You can use them as often as once a day, though two to three times a week is great too.