I purchased this carrier for a 2 leg international flight with my 16 lb boston terrier.  She had never flown before, and we were both nervous about how it was going to work out.  Choosing this carrier made our trip a breeze!!  I trained her to associate being in it with getting treats, and then we practiced riding  around in it on our normal walking path at home. For the long trip she was snug but comfortable, both while riding around the airport in it and while under the seat on the plane.  I was able to unzip it a bit to stick my hand in with treats and pets when needed.  Thanks for such a great product!!