Dow STYROFOAM™ extruded polystyrene Buoyancy Billets are an excellent choice for floating structures such as docks, rafts and boathouses. STYROFOAM Buoyancy Billets consist of millions of tiny closed-cell air bubbles. That makes it extremely buoyant. It also means structures cannot become punctured or water-logged. Buoyancy billets are lightweight and easy to install, so structures can be built quickly and efficiently.