The material isn’t paper thin and I love how the blind smoothly glides up. Yes, it does let in some of the sunlight on the sides.. but I think that is normal for most blinds that are mounted on the inside. Maybe if you were to mount the blinds on the outside and order a larger size than your window it might let in less light, if any at all, but it all probably depends on where you’re planning on placing them. For my window, the outside mount wouldn’t have looked too good so I decided that I’d mount the blind on the inside with the exact width measurement of my window.