Okay... if we're talking about using a Limp Membrane in combination (lamination) with other building materials... SKIP IT!! This type of buidling material CAN be very helpful, but the listed STC numbers are misleading. The membrane itself has decent numbers when used MONOLITHICALLY... not attached or sandwiched between anything else... If you are creating a multiple layer boundary wall, stick with Gyp Bd, MDF and other "heavy" materials. It's a mass thing, not a limp mass thing... Hmmmm.. that's what I told her!!