Abstract: A packaging body for heat processing a material retained therein is basically formed of a plastic base material having side joining sections, and end sides. The side joining sections and end sides are superposed and connected together to form a bag for filling the material. A sealant layer is deposited on at least one of the end sides to connect the end sides together through the sealant layer to thereby form a vapor communication joining section at the end sides. The sealant layer has a peeling off property from 0 to 1,200 gf/15 mm at 90° C. and a peeling off property of equal to or more than 3 kgf/15 mm at a room temperature. Thus, only when the packaging body is heated more than 90° C., the vapor communication joining section is only opened to release pressure inside the packaging body.