Abstract: A flexible liner has a planar base and multiple sides extending up from the planar base. The base and sides of the flexible liner define a cavity for receiving foodstuffs or other items. The flexible liner is generally dimensioned to fit within a cavity of a flexible container bag, such as a soft-sided cooler, duffle bag, gym bag or reusable grocery tote bag. The flexible liner provides increased rigidity and durability for the flexible container bag. While manual force deforms the flexible liner from its original shape, the liner is elastic and has shape memory such than when the force is removed, the liner will return to its original shape. The liner is made from a viscoelastic polymer material. Further, the liner can be attached to or configured to be removable from the flexible container bag.