Variable displacement base and container and method of using the same

Hot-fillable plastic bottle including a finished portion, a body portion with at least one circumferential rib configured to resist radial distortion, and a base portion. The base portion comprises a base sidewall, a bottom support surface extending radially inward from the base sidewall and defining a reference plane, an inner support wall extending upwardly from the bottom support surface, and a diaphragm extending radially inward from the inner support wall. The diaphragm comprises an inner wall having an arcuate shape with a radius r1 and a central conical structure, where the diaphragm is in an initial as-formed position with the conical structure above the reference place. The diaphragm is configured to move from an initial as-formed position toward a second position when an internal pressure relative an external pressure exceeds a threshold value.