a thermoformable acoustic sheet material that is lightweight and provides excellent sound attenuation over a wide range of frequencies includes a combination of sound attenuating materials , including an acoustic barrier having a relatively high density , a thermoformable sound absorbing layer having a relatively low density , a substantially air - impermeable layer between the barrier and the sound absorbing layer , and an acoustic performance enhancing scrim or perforated thermoplastic film on the opposite side of the sound absorbing layer . the combination is useful for preparing contoured acoustic treatments for reducing sound transmission from the engine compartment of a vehicle to the passenger compartment of the vehicle .