AeroMat Peanut Shaped 50cm Blue Fitness Ball

* anti-burst design * easy direction controlling, great for kids and seniors * offers moderate instability, only rolls in one direction (forward and backward) * 50 cm. size is measured from the lowest point on the curved surface of the ball * manufacturer suggests inflating the ball 80%, letting it sit overnight to allow for expansion, then adding the last % of air * warranty: manufacturer's discretion