Description Impact Isolation Class (IIC) for Hush ll is 78. this rating is for impact noise, like moving chairs, sofa, table or other furniture, footfalls, things dropping on the floor and so on. Sound Transmission Class (STC) for Hush ll is 73. this rating is for the ambient sounds like music or voices. Hush ll Underlay has superior sound absorption, premium sound ratings and also has a vapor barrier.
