A fully collapsible shipping container is comprised of it least one sheet of a flexible, thermally insulating material. The sheet or sheets of material have mutually parallel linear side edge fastening margins. The sheet or sheets are folded to form a rectangular floor and four walls projecting from the floor in orthogonal relationship relative thereto to define an enclosure. The linear side edge fastening margins meet at and are heat sealed throughout interfaces of mutual contact. The side edge margins are directed outwardly from the interior of the enclosure. The heat seals formed by the two layers of material at the edge fastening margins are leak proof so that moisture cannot escape from perishable food products shipped within the container. A container can be formed from a single sheet of plastic bubble packing material or from material lined with a plastic film and shaped so that the container will fit within an outer corrugated paper board box. Alternatively, a container can be formed from a single sheet of plastic bubble packing material having a metallic reflective layer on its outside surface to accommodate an inner corrugated paper board box placed within the container enclosure. In still another embodiment the container is formed of several sheets of moisture impervious material having fastening edge margins that are heat sealed together to form a leak proof enclosure.