These blinds are definitely black out and keep the hot sun from baking a room during the day. One comment and suggestion I'd make is that if you're measuring for an inside mount, I would not subtract the 1/2" off the total any more since these blinds run true to size. If it says 25 1/2, it's 25 1/2. I made the mistake of thinking there was some sort of extra space needed on the sides like Roller Shades, but there is not. Measure and pick the size that is closest to your window width. It looks fine with the 1/2" subtracted, but it would have been better had i not subtracted it and there would be less light on either side of the shade. Overall though, very pleased. Easy to raise and lower, and the installation was simple to follow.