The opaque stripes here are true blackout fabric, so lining them up closes the window down to as dark as a striped blind can get. Slide the layers apart and you are back to filtered daylight — the reason to buy this rather than a plain blackout roller is that you keep both states on one blind.

Be clear about one thing: the stripes are blackout, the join lines between them are not perfect, and a mounted blind still has edge gaps. For a true sleep-dark room, mount outside the frame.