The barrier materials covered by this specification are intended for use in specialized military methods of preservation. The combination of all performance characteristics of MIL-PRF-121; flexibility; waterproofness; contact corrosivity; greaseproofness; seam strength and fabrication; puncture, bursting, aging, blocking, and curl resistance; delamination; water resistance of markings provide the necessary requirements for protection from exposure to the extremes of the navy/naval aviation environment. Navy/naval aviation items are exposed to high moisture, high salt concentration, transfer at sea, rough handling, and minimal storage conditions. There are no commercial equivalents that meet the physical, mechanical, and corrosion requirements necessary to protect materiel that is exposed to the operational naval aviation environment. Specifically, MIL-STD-2073-1, Methods of Preservation 20 and 33, use MIL-PRF-121 as a primary source of barrier materials that provide waterproof and greaseproof protection for applicable items encountering the above conditions. MIL-PRF-121 provides one of the building blocks for applying specialized military preservation techniques approved under MIL-STD-2073-1.