A plastic container that is adapted for adjustment to internal volumetric changes such as those that occur as a result of internal pressure and temperature changes during the hot-fill process includes a container body defining an internal space. The container body has at least one flexible panel defined therein, which includes an outer flexible panel portion and an inner flexible panel portion. The outer flexible panel portion has a shape when a pressure equilibrium exists between the internal space and ambient external pressure, and is further constructed and arranged to assume a shape of increased concavity when a sufficient underpressure exists in the internal space. The inner flexible panel portion is constructed and arranged to flex relative to the outer flexible panel portion in order to accommodate internal pressure changes within the container body. The inner and outer flexible panel portions accordingly work in tandem to permit efficient vacuum uptake in a hot-fill type container. In addition, a boundary between the outer and inner flexible panel portions is preferably entirely curved.