Abstract: A system for selectively interposing particulate insulating material in a cavity of a transmission or window panel assembly employs an upper aperture into the cavity through which the insulating material enters and is removed. A flow diverting means adjacent the aperture diverts positive pressure air flowing toward the cavity into the ambient atmosphere, and the momentum of the insulating material causes it to continue through the aperture and fill the cavity. Suction pressure air flow out of the aperture removes the insulating particles, and ambient pressure air flows into the lower portion of the cavity through vents to lift the insulating material upward out of the cavity. The flow diverting means confines the suction air flow out of the cavity to the conduit or communicating means connected to the aperture.