**Snoozer 4-in-1 Roll Around Travel Dog & Cat Carrier Backpack with Wheels - Convertible Pet Stroller, Travel Bag for Small Pets Up to 15 lbs (Black, Medium) - Perfect for Air Travel, Hiking & Daily Outings**

UPDATE 6/28/2016Since buying this 2 years ago, have used it on several domestic flights mainly with Southwest, and I can confirm that the large one does fit under their seats. I have the Large one. Make sure your particular dog fits in the bag, though. At check in, if they question you (only happened to me once) you can show them that it is collapsible once the removable base is off. When walking thru airplane isle, may be easier & quicker to just carry it, rather than roll it. As for durability, material has endured, without a scratch. Just be careful that bottom plate is attached correctly when moving around. Otherwise, it will be damaged.So convenient and versatile. From backpack, to rolling, to under seat.Very convenient carrier for medium breeds, up to 9,5 kg ( +/- 20 lbs.) My dog is a Miniature Schnauzer, with a large frame for his breed and he was relatively easily transported thru airports, gates, on board, etc. Most of the time I had the carrier flat in waiting areas, and he conformed just fine, no troubles. He was comfortable. If it was possible, I did let him have some breathing space and allowed him to have his head out and watch the world go by. Having said that, my particular pet is quite easy-going with a very predictable temperament. Non-aggressive and sociable and very physically flexible. And not a whiner.I did fly with Air Canada, (relocating from south Europe to US) due to the maximum weight allowances for pets, (10 kg) and selected Premium Economy, from Europe to Toronto. In an aisle seat, the carrier was not easily tucked under the front seat, however, even with taking out the removable base. I had to give him to my son, who was seating across the aisle in a window seat, so that it could squeeze in with more room to spare. I have to say that he was seated next to a very kind man, who did not mind relinquishing some of his leg room.Flight from Toronto to the US, on a much smaller aircraft, ironically the leg room was much more spacious in regular Economy. More room to spare, so you might take that into account. The difference being not on the overall dimensions, but in the structure of the premium economy seats. The legs of the front seat were much closer together, leaving less room available.That said, the crew was not at all bothered by the minor trouble when boarding. They even offered water for him. But again, no one even realized that there was a dog on board. We were able to very discreetly pet him to reassure him, feed him, etc and he laid flat mostly sleeping the whole 10 hour flight.Carrying it throughout the terminals, you do need to be careful switching positions from flat to standing, if you have a heavier dog, as you can lose the balance if you do not control your movements. Steady and slow when switching. And my dog, as said before is a tall and long dog for his breed, but very lean and flexible.The construction material is very durable, just make sure you put some kind of blanket for warmth and padding. The handle is sturdy as well.All in all, a really good purchase worth the money (and I had to pay a high delivery charge, on top) because apart from being a breed that is instinctively highly anxious during times of separation, he does have a heart valve dysfunction that causes rapid palpitations and I did not want to put him through the ordeal of cargo shipment if I had a choice, especially during the summertime. Highly recommended..