The AIR PLUS is a pet carrier built by you! The design is based on years of research and feedback from loyal customers. With additional storage, padding and ventilation the AIR PLUS is built for intermediate hikes, bike rides or any moderate outing you can dream up. Like all K9 Sport Sack® models, it was designed under the close direction of veterinarians, dog trainers and outdoor product engineers to be ergonomic, safe, and strong. 40 LB/18 KG weight limit.