The Plus 2 is a backpack dog carrier with a multi-functional storage pack. The storage pack is great for bringing gear, treats, or other necessities along on your adventures. It also acts as a support for your dog's back, pulling your pup in snuggly against your back. Available in sizes S-L, its thicker shoulder straps and padded back panel allow for more weight and strenuous activities. The Plus 2 is our most complete carrier for small to medium sized dogs and fits dog owners small to large in build. For Dogs Ranging 8-40 lbs (4-18 kgs) Plus 2 sizing: S 13-17 inches, M 17-20 inches, L 20-23 inchesAll K9 Sport Sack carriers are specially developed under the close direction of animal professionals, veterinarians, dog trainers, and outdoor product engineers to be ergonomic, safe, and strong.