There is disclosed a sealable, flexible membrane for encapsulating a part to be isostatically pressed at an elevated temperature. The membrane includes at least one first layer of polymeric film having a melting point above the elevated temperature, and at least one second layer disposed on the first layer. The second layer comprising a metal. In one embodiment, the metal comes into contact with the part to be isostatically pressed. The membrane, which typically has a thickness ranging from 10 to about 500 μm, and is impermeable to the flow of liquids and gases when sealed, can be used to warm press parts up to about 350° C. and pressures ranging from 5,000 psi to 100,000 psi. Methods to isostatically press parts using this sealable, flexible membrane are also disclosed. Bags made from the sealable, flexible membrane that are used in isostatic presses are also disclosed.