$39.50; https://www.ventapak.com/
Designed as a lightweight, adjustable, and low-profile accessory to fit all standard-sized backpacks, VentaPak transforms wearing a pack into a more comfortable, cool and dry experience by creating a space for airflow between a person’s backpack and back. Composed of a polyester hexagonal mesh screen secured on flexible spring-steel frame, the VentaPak securely attaches to the backside of any standard-sized backpack by using special attachment mechanisms with buckles and adjustable straps. At just 12 ounces, the VentaPak’s frame is covered with a soft and malleable neoprene foam, providing a comfortable fit that not only offers superior ventilation by separating your pack from your back, but also improves posture and back ergonomics by gently tugging shoulders back and providing lumbar support. The mesh screen also distributes pack load more evenly and comfortably across the back, keeping objects, especially non-flat ones, from pressing and digging into your back.