Disclosed is a releasably sealable bag for low temperature cooking comprising a film material, wherein the film material does not deform at temperatures of up to about 125.degree. C., and wherein the bag is air and liquid impermeable when sealed. Also disclosed are such bags wherein at least a portion of the film material is comprised of a composite film material provided with a pressure sensitive adhesive protected from inadvertent adherence. Further disclosed are methods for food preparation and cooking using any of the embodiments of the bag of the present invention.