Completely blocks out light! This blackout sheet was created by Aya Aiba, a sleep consultant for infants and young children. One of the important points for putting babies to sleep is the "sleep environment," and "light" is a key factor. When consulting about sleep, I always ask, "Is light leaking in?" It's crucial to ensure no light enters and that the room is properly blacked out. From the official website This is a set of two blackout sheets supervised by Aya Aiba. 99.99% blackout rate (according to the official website) Used for about a year and a half. Selling due to moving. They show signs of use, with wrinkles and holes in the vinyl at the top, but please purchase if you don't mind. No returns accepted. #InstantPurchaseOK #AyaAiba #SelfSleep #Nentore (Sleep Training) #BlackoutSheet