Acoustic foam is an open-celled, lightweight material made from polyurethane foam (either polyether or polyester). It can be attached to walls, ceilings, doors, and other features of a room to control noise levels, vibration, and echoes. Acoustic foam is usually cut into tiles which are suited to placing on the walls of a recording studio or similar environment to deal with mid and high frequencies. It can be made in several different colours, sizes and thicknesses. Many acoustic foam products are treated with dyes and/or fire retardants.