Once the two ingredients have been combined to form hot liquid polyurethane, they are passed down through a pipe into a nozzle head. Beneath the head is a series of rollers upon which waxed paper[paper?:paper sample maker cutting machine] passes by. The nozzle jets a fine spray of hot liquid over the waxed paper, mixing with blasts of carbon dioxide coming from another nozzle. This causes the polyurethane to expand as it moves down the conveyor belt, forming a foam strip. The edges of the foam are trimmed and compressed to ensure it retains a viable shape. The foam is comprised of an untold number of tiny gas bubbles trapped in the polyurethane. Unless the gas is released, the foam will take on the consistency of a rock. So, the foam passes beneath a series of heat lamps. It dries the foam and causes the bubbles to expand, then burst, leaving a completed spongy porous material behind.
