Abstract: A diffuser assembly for an air-conditioning installation, has low thermal conductivity so that it can prevent from accumulating condensation and is incombustible enough. Each of the diffuser elements of the diffuser assembly contains 90% by weight or more of an inorganic fiber material or an inorganic material composed mainly of inorganic fibers and obtained by molding and curing with the use of a binder. The inorganic fibers used are preferably ceramic or polycrystalline mullite fibers.