MIL-PRF-121G, PERFORMANCE SPECIFICATION BARRIER MATERIALS, GREASEPROOF, WATERPROOF, FLEXIBLE, HEAT-SEALABLE (30 APR 2001) [SUPERSEDING MIL-B-121F]., This specification establishes the requirements for heat-sealable, greaseproof, waterproof, flexible barrier material used for the preservation of military supplies and equipment (see 6.1).