Very good for those that don't or can't take out their AC's for the winter months. I bought this for my 24,000 BTU AC that is a massive pain to take in and out. You definitely don't want to just rely on the somewhat flimsy strap and clip that comes with it though. It would not stay on the AC during a very windy storm. But if you use duct tape or bungee cords around it, it will definitely stay on. It's pretty thick too, and it's doing a great job keeping air out of the house and also helps keep the unit reasonably dry. If you use this on the outside and then use the shrink wrap plastic kits from 3M on the inside, you'll be in great shape to keep the cold air out during the winter months.