The term sound proof foam is another one of those misnomers. There is no foam on the market that is soundproof. I know this to be true because I have been manufacturing foam for 10 years. Lets pull apart these terms “sound proof foam” and examine them individually.
The term soundproof means to keep sound from entering a room from any outside source and to keep sound in the room from leaving the room and entering adjacent structures. Foam does not possess the physical properties necessary to stop this type of sound transmission. Foam is not dense enough or rigid enough to provide the mass and structural stability to stop middle and high frequencies, let alone have any impact on bass energy. It would take a piece of foam 11 feet thick to absorb all the energy of a 100 Hz. wavelength.
The terms sound proof and foam should never be used together. Foam is not used to sound proof anything. There is no such thing as sound proof foam. Foam is an acoustical tool that can absorb energy within a contained room. It can be used to control unwanted room boundary reflections, so the listening position is free from unwanted reflections and our ears can focus on the direct energy from our loudspeakers. Foam can be used to absorb and minimize the unwanted energy from another individual who is telling you to turn your stereo down. A better approach would be to place that individual in a soundproof closet.