This was easy to cut to size (my window is 35 in wide) and easy to install. It completely blocks light except for a small amount of light coming in from the sides. However, I installed it behind wood slat blinds and with the paper shade down and the wood slat blinds angled shut, absolutely no light enters the room. It is pitch black. Perfect solution to making the room dark for grandbabies to sleep in when visiting! MUCH better than taping tin foil all over the windows which we had to do the last time they visited.