Abstract: An improved lightweight diffuser assembly having a plenum chamber formed of fiberglass laminae is provided. The diffuser assembly is universally adapted for interfacing with various size conventional ducts of an air delivery system. The plenum chamber has a variable density across its surface and further includes a fibrous textured interior surface to optimize the sound absorption characteristics. Sheets of laminae fiberglass impregnated with uncured phenolic binders are placed in an appropriate die mold cavity and subjected to both compression and heat. The plenum chamber is cured in approximately a temperature of 700.degree. F. to 900.degree. F. for a time period of approximately 25 to 45 seconds to provide an interior fibrous textured surface. Carbon black and an interior sealing sheet can be introduced into the fiberglass laminae prior to compression.