This backpack is slightly larger than others on the market. My 10 lb dog fits in a smaller backpack, but was scrunched. In this backpack, he can sit up fully and curl up in the bottom to sleep. It has several openings for venting. When it's cold, there is room for me to stuff a blanket or my sweatshirt inside for him to crawl under. The bottom forms a stiff floor so the backpack doesn't sag and he has the full bottom as usable space. It also has a chest strap and a waist strap which allows it to fit very securely, as I use it to take my little buddy with me when I'm on my motorcycle. I have only been using it for a short while, but it appears durable to me.