Abstract: The inventive method comprises compressing roughly half a bun of polyimide foam at a rate of no more than 12 feet per minute from its initial height of approximately 15″, until it reaches a compressed height of no more than 2″. The compression is maintained on the bun for no more than one minute, and then released. The half-bun is then permitted to expand, and it will rebound to approximately 90-95% of its initial height. This conditioned foam may then be cut or otherwise formed into acoustical panels of varying heights and/or configurations, without worry about the ultimate shrinkage after treatment. In addition the treated half-bun may be cut into irregular shapes of more varying dimensions, up to the maximum dimension of the treated half-bun.

Abstract: Lightweight acoustic absorbers. The acoustic absorbers absorb energy during launch of a vehicle by a rocket, and are adapted to line the inside of a cavity of a fairing containing a vehicle. The absorbers comprise acoustic absorbing members, and a layer substantially surrounding the acoustic absorbing member which is substantially impermeable to contaminating particulates found within the fairing, and substantially impermeable to any contaminants which may be emitted by the acoustic absorbing member. A plurality of vents are cut in the layer, and a filter is placed over the vents to filter out any contaminants. The vents allow the gases within the fairing and the acoustic absorbing member to pass therethrough, thereby compensating for differential pressure.