Acoustic Foam Panels
Foam panels are the cheapest and most widely used type of acoustic tiling. Made from poly-urethane filled with air pockets, they are attached to the walls in sheets to absorb sound. They are the preferred method in most many studios, as they look professional, and they tend not to clash visually with the rest of the black equipment, mic stands, speakers, amps, black-clothed musicians etc.
Different densities of acoustic foam are used for different situations. A dense, thick, broadband foam will be better at reducing bass reverberation in a room, while a thinner foam can be used effectively to reduce high-frequency sound reflections in a room, particularly when applied to ceilings in high rooms.