My apartment has a west-facing window that radiates a tremendous amount of heat in the afternoon even with curtains drawn, which puts a huge amount of strain on my AC unit to counteract. I used this product to cover the window, and it worked astoundingly well! My curtains remained cool to the touch even in the middle of the afternoon, and my AC unit was under much less strain. I could not use the suction cups because my windows are opaque and bumpy, so I instead used some S-shaped hooks from Daiso to attach the sheets to the curtain rail.