NOTE: Each sheet is 24" x 27"
NoRez is a damping material developed specifically for loudspeaker applications and in particular the functions of dampening and eliminating enclosure resonances.
With nearly all loudspeakers there are areas of the enclosure that will resonate while playing. Many speakers allow large unbraced panel areas to be greatly excited and create resonances not present in the original music. Some loudspeakers are well braced and are even made from thicker than average material to minimize resonances, yet enclosure resonances can and will exist.
NoRez is designed to greatly attenuate such resonances using a thick layer of damping material that is treated with PSA. The damping layer of NoRez is many times thicker than most that you will find in a loudspeaker.
The heavy damping layer of NoRez not only adds mass to the enclosure but it is comprised of a non-resonant material that effectively kills the resonance and greatly quiets the enclosure so that you hear the music and not the box.
The second layer of NoRez is a 1" thick layer of open cell foam, with a textured surface, designed to absorb standing waves and internal reflections in the enclosure.
Many other aftermarket products used in that application often suspend a barrier layer sandwiched between foam layers. This can have some isolation benefit, but does little to control enclosure resonances.
This isolation layer is typically used in noise control pads to keep sound in some frequency ranges from passing from one side of the barrier to the other. This is typically used in industrial applications to reduce sound produced by noisy machinery. This can sometimes have an adverse effect in some loudspeaker designs if used with heavy coverage as the suspended layer can mass load the woofer to some extent.
Some material sold for use in loudspeakers incorporate this sound barrier layer with no damper at all. It has little to no effectiveness in resonance control. While some of these barrier pads may cost very little, using it in a loudspeaker can often be of very little value other than its effectiveness to absorb internal standing waves with its open cell foam layers. If it has no damping layer then it will not be effective for resonance control!
So mass load your enclosure and not your woofers, and don't settle for less.