A door system comprises a door panel, a support member, and a pivoting vertical plate. The door panel comprises a plurality of discrete rigid insulation pieces interposed between flexible layers. An outer skin encompasses the rigid insulation pieces and the flexible layers. The door panel is secured to the support member by the outer skin, such that the outer skin bears the weight of the door panel. The vertical plate is secured to a trailing side of the door panel. The vertical plate includes keepers that selectively engage hooks extending from a casing positioned at a doorway. The rigidity of the door panel depends on the pivotal position of the vertical plate relative to a plane defined by the door panel. The door panel provides sufficient flexibility to withstand impacts from objects and vehicles yet also provides sufficient rigidity to insulate a cold environment from a warm environment.