These are wonderful insulators to reduce heat loss at windows. We have them on eight windows at our vacation home. In the summer we use them to keep the bedroom cool, And in the winter we use all of them to reduce our heating expense, at least at night. We got the room-darkening variety but they also have some that let more light through. We’ve been using them for three years now and recommend them. The measuring was a little challenging — they fit very tightly to provide their insulation. And we got some help to install them. But they absolutely work as promised. Highly recommended.