A plastic container has a base portion adapted for vacuum absorption, the container including a base and a body extending up from the base along a central axis to a finish portion defining a mouth. The base includes an outside wall, a chime connecting the outside wall to an annular contact ring, an inside wall extending upward from the contact ring to a hinge, and a diaphragm connected to the hinge. The diaphragm can move between first and second positions in response to pressure change within the container. The diaphragm includes a central region and a flexible wall having a curved profile in cross section. The flexible wall curves downward from the hinge to the central region. In some embodiments, the flexible wall is asymmetric and includes a first portion having a curved profile and a second portion having a linear profile. A container wall structure is also disclosed.