Two different problems, two different materials
Soundproofing = stop sound from crossing a boundary. Between rooms, between floors, between your home theatre and the sleeping baby. This needs mass (MLV) and decoupling (resilient channels, double drywall).
Acoustic treatment = shape the sound inside one room. Kill echo, tame flutter, tighten dialog. This needs absorbers (foam, PET, wood wool) placed on the surfaces where sound is bouncing.
Foam on drywall does not soundproof
Sticking acoustic foam onto a wall does nothing to stop your neighbours hearing you. Foam absorbs the sound already in the room; it doesn't add mass to the wall. This is the single most common misconception we correct on customer calls.
For real soundproofing, mass has to go inside the wall — MLV under drywall, or a second layer of drywall on resilient channels.
Most projects need both
A home theatre needs isolation (so it doesn't wake up the neighbours) and treatment (so the movie actually sounds good). Same with recording studios, hotel rooms, and cinemas.
The right ratio depends on the room. Acoustimart specifies both stacks together on project-scale enquiries.