MAXIMUM AIR CIRCULATION & MULTIPLE ENTRANCES: Mesh windows on 4 sides for optimal airflow, 4 entrances (sides, front, and back) allow your pet to enjoy the outside scenery and easy entry into the carrier, and 1 expandable soft mat to keep your pet comfy during the journey. EXPANDABLE & COLLAPSIBLE: This pet carrier backpack with an expandable back allows your pet to move around more comfortably. And the carrier can collapse flat when not in use. Measures 13x9.8x16.5 inch, easily fits most small/medium-sized pets, weighing up to 18 lbs. Each airline sets their own specific requirements, so it is advised to check with your airline of choice. STURDY & SAFETY: Equipped with a durable rod on the top and both sides are fixed with frames to stabilize the structure, plus a firm bottom pad offers solid support for your pets. Also comes with a safety leash to prevent escape, this pet backpack carrier is sturdy and safe for your pets. COMFORT DESIGN: Made with quality and water repellent 300D Oxford fabric for long-lasting use. 2 side pockets to store pet supplies and a ROLLER BLIND can be pulled down to protect from the sun. The travel backpack carrier is portable for traveling, camping, hiking, biking, going to the vet, or walking in the park.