We used two of these for our two dogs on their first flight, which was fairly long (over 5 hour flight on United Airlines). Our dogs are each about 5-6 pounds and they had more than enough room to turn around and lay down in the bags. I'm not sure larger dogs would be as comfortable. The bags fit well under the seats of the United planes we boarded (note the flights with seat-back screens sometimes have less space under the seats so we had to turn one of the bags for that flight) and the dogs were comfortable the entire flight. There are several useful pockets on the side and ends of the bag which were handy for stashing things like mini wee pads, collapsible bowls, treats, etc. There was sufficient mesh over the top and sides of the bag so the dogs didn't overheat. The top opening was also large enough so that it was easy to maneuver the dogs in and out during the security checkpoints. The bags seem very sturdy and well-made but are very lightweight. The sides are soft, but still structured and rigid and don't flop over. The bags can be carried three ways: they have an opening that fits easily over luggage handles, they have a nice wide handle on the top to alternatively, carry by hand, and there is a long shoulder strap. The pad that comes with the bag was plush and had a nice cozy covering which is machine-washable. The bags also had no weird smells (we purchased a different travel carrier from another brand previously, which had a really awful, strong chemical odor). The chocolate color was discreet and didn't scream "dog inside!" The bags also were easy to secure with seat belts in the car.The only things that would make this bag even better: the zippers on the top of the bag were a little difficult to zip up and over the top corners; if you want to fold up the top sides of the bag to allow your dog's head to stick out, the velcro that secures the top (which folds underneath the top handle) is not strong enough/or is not positioned well, so that one side kept falling down; and the long shoulder strap has a padded portion which is difficult to position over your actual shoulder.All in all, this was a great buy and we are happy to be able to travel comfortably with our dogs! The price is a little steep but the quality makes up for it (we've probably spent the same amount of money on various previously purchased carriers which didn't work out).