Acousta-Stuf Polyfill Speaker Cabinet Sound Damping Material 1 lb. Bag Acousta-Stuf is a synthetic material made from crimped fibers. It is an excellent choice for filling small enclosures or transmission line cabinets. Acousta-Stuf will also outperform Dacron, foam, and fiberglass. Acousta-Stuf is a sound absorption, dampening fiber that will deepen bass and more!