It’s expensive but worth every penny.
I have had my Freedom Pet Insulated Door (RANGER Pet Door) for many years, and it works well. keeps the cold out, and keeps my dogs happy. My door is Large, and it has worked beautifully for all sizes of dogs, down to a 12-pound chihuahua mix. For the last two years, it has gotten a daily workout from my obsessive Border Collie Mix, who dashes in and out at full speed countless times each day. I live in northern Vermont, and this door absolutely seals the cold out in winter. I have had many different dog doors through the years, and this one is THE BEST. It is very durable,. works well, and has GREAT customer service. The outer flap recently came loose on one side, and I emailed the company and they responded immediately with explicit instructions. The fix took me all of about 2 minutes, and I’m not particularly handy.