Variable displacement base and container and method of using the same

A method of hot-filling a plastic bottle, the method comprising:

• providing a plastic bottle, the bottle comprising:
• a finished portion defining an opening,
• a body portion disposed below the finished portion and defining a central longitudinal axis, the body portion comprising a body sidewall defining an interior, the body sidewall having at least one circumferential rib extending about its circumference, and
• a base portion disposed below the body portion, the base portion comprising:
• a base sidewall,
• a bottom support surface extending radially inward from the base sidewall toward the central longitudinal axis and defining a reference plane,
• an inner support wall extending upwardly from the bottom support surface, and
• a diaphragm extending radially inward toward the central longitudinal axis from the inner support wall, the diaphragm comprising an inner wall having an arcuate shape in a side cross section with a single radius r1 of constant dimension and a central conical structure, wherein the diaphragm is in an initial as-formed position with the conical structure above the reference plane;
• filling a portion of the bottle with a hot-fill liquid having a temperature above an ambient temperature;
• and
• sealing the opening, wherein the diaphragm moves from the initial as-formed position toward a second position when an internal pressure of the sealed bottle relative an external pressure external of the sealed bottle exceeds a threshold value.