The benefits and popularity of frameless soft sided pet carriers is their pliability and ability to conform to varying seat configurations of modern aircraft. All airlines actually have similar sizing requirements, and those are more stringently applied to the older hard shell pet carriers. All airlines will require your foot space to be cleared for takeoffs and landings, and your pet to stow under the seat in front of you. Virtually all airlines set their seats at an 8.5" (21.6cm) height, although that will vary some with differing aircraft models and even where one sits. Most of my models ( not the Rhodium ) are easily pliable to be able to accommodate your pet with maximum space but yet conform to fit under the 8.5" seat. Keep in mind, airline capable carriers are designed for your pet to be laying down, as most pets will need to do so to allow for fitting under the seat.
I always focus firstly on pet safety and comfort. I am never satisfied with any of the models, all are a constant evolution and I improve each with every production run over time based on user feedback and testing. There is a fine balance for soft sided pet carriers as we need it to be pliable for airline under seat compliance but also structured well for those times when we aren't in the air.
Be sure to look over the FAQ page for more answers to common questions, and feel free to contact me at: firstname.lastname@example.org for questions.
Michael @ Mr. Peanut's