The K9 Sport Sack FLEX is the most up to date, upgraded, ultimate dog carrier backpack. With its FLEX 3-1 sizing technology, you can adjust your dog to get the perfect fit. Our team also added a waist belt to help distribute the weight of your dog and added extra comfortable shoulder straps to help out with the heavier load capabilities. The colors blue and green were chosen for their reflective purposes that will help you and your dog stay as cool as possible on your adventures.