Designed for superior flotation and long lasting service, Dockmate Float Drums also make it simple on the do-it-yourselfer. Thick mounting flanges and slots provide easier installation, while ribbing adds strength and durability. Rotationally molded seamless outer shell is filled with expanded polystyrene foam for maximum buoyancy. Self-venting plug allows hot air to escape. The unique reflective Flash Dot is easily seen at night to take the guess work out of nighttime docking. 15-year warranty.