Belgium research and development utilizes the molecular structure of the modified polyurethane foam to enable it to absorb the specific sound of car noise.
The researcher uses a computer sound spectrum analyzer. The instrument can show that as the molecular structure of the foam changes, its resonant frequency also changes, and the sound it absorbs also changes.
The researchers changed the polyurethane by controlling the weight of the polymer chains of the molecules and the number of bonds that connect them. The shortening of the polymerization process results in shorter chains and more rigid foams. Harder foams absorb higher frequencies of sound.