There are two basic core foam choices when selecting acoustic foam for your sound control needs.   Open cell polyurethane foam or open cell melamine foam.   First, note that closed cell foam does not absorb sound, the pores of the foam do not collect sound wave energy, the foam must be open cell.   Second, the difference between Polyurethane and Melamine foam is in the fire rating.   Melamine foam is class A fire rated, approved for use in public venues such as schools, churches, hospitals and so on.  Polyurethane foam is class B fire rated, this means the foam is self extinguishing, and typically approved for use in private settings such as industrial, commercial office, and music studios.   Class B foam is not to be used in public venues or near open flames or high heat sources.  From either of these core foam raw material options, there are then differences in how the foam is cut into panels, how the foam is sculpted, how thick the panel is and so on.  For help in selecting your best foam option for your acoustic needs, call to 1-800-638-9355 or visit NetWell Noise Control online at www.controlnoise.com.