Air 2 Original Backpack Dog Carrier**Select styles and sizes below are out of stock and may be available for Pre Sale. Ships by Oct 5th. Unavailable: Jet Black: XS, S, M Light Grey: S, M (pre sale) Sumer Mint: XS, S The Air 2 by K9 Sport Sack is a durable, breathable dog carrier backpack designed for small to medium sized dogs. This mid level carrier offers the ideal balance of comfort, support, and value perfect for daily walks, moderate hikes, bike rides, and public transportation.