This pet life jacket has the same buoyant EVA foam used in coast guard approved personal flotation devices. Made by wetsuit pioneers Body Glove, the life jacket straps comfortably to the pet's torso and positions the buoyant molded foam over the its back and under the chin, ensuring the torso and head remain above the waterline. The undercarriage is made from neoprene--the same material used in scuba suits for its elasticity and durability--that contours to the body without restricting the pet's ability to paddle. The jacket has reflective strips stitched into the exterior, three adjustable straps ensure a proper fit, and an integrated handle on the top of the jacket helps you lift the pet into a boat. Size is determined by the dog's weight and the distance from the base of its neck to the base of its tail: XS (9"-11" and under 15 lbs.), S (11"-13" and under 20 lbs.).