Will regular foam work for soundproofing a room?

Answer 1

No. Regular foam will not work for soundproofing a room.

There are two types of soundproofing materials - sound blocking and sound absorbing. Materials like foam are usually considered sound absorbing because they are porous and prevent sounds from leaving a room. Unfortunately, porous materials really aren't effective at completely absorbing or blocking any type of noise - especially foam.

Your best bet is to get something like Quietrock. It is one of the most popular soundproofing materials on the market today and has both sound absorption and sound blocking properties.

Whatever you choose, do not under any circumstances use materials without knowing and corroborating their resistance to fire. You could seal yourself in a chamber that is engulfed in flame in moments, risking injury/death to yourself and others in the building. Another threat when using improper materials is the poisonous gas they could give off, in a fire.