A noise insulating structure for a passenger compartment of an automotive vehicle. The noise insulating structure comprises first, second and third sound absorbing materials which are disposed respectively to a head lining, a dash insulator and a floor carpet disposed in the passenger compartment. The first sound absorbing material is capable of absorbing sound within a first frequency range of from 0.8 to 10 KHz. The second sound absorbing material is capable of absorbing sound within a second frequency range of from 0.3 to 2 KHz. The third sound absorbing material is capable of absorbing sound within a third frequency range of from 0.1 to 1 KHz. Each sound absorbing material is formed of a unshaped polyester fiber mixture which is prepared by mixing polyester (main) fibers and binder fibers for bonding the polyester fibers to each other.