Folded Covers are often used in applications requiring the cover to be air and light tight, such as laser bellows. These covers can also be used in applications requiring bellows to be able to handle internal or external pressure and motion. Folded covers can be constructed out of elastomer or thermoplastic materials. Square or rectangular designs can be tapered, including offset configurations. Folded bellows are available as an enclosed-shape bellow in any flat-sided form (all shapes except round). An alternative, lower cost option is a single-layer folded construction, made from thermoplastic film.