PROBLEM TO BE SOLVED: To provide an article of footwear including a chamber configured such that the compression of the chamber increases, however, the stiffness of the chamber increases in a corresponding manner. SOLUTION: The article of footwear has an upper and a sole structure secured to the upper. The sole structure includes a fluid-filled chamber and a polymer foam material surrounding at least a portion of the chamber. The chamber includes a first surface, a second surface on the opposite side to the first surface, and a sidewall extending between the first surface and the second surface. The first surface, second surface, and sidewall define a plurality of lobes radially extending outward from a central area of the chamber. The polymer foam material defines part of the side surface of the sole structure of the footwear, and distal ends of the lobes are exposed to the side surface of the sole structure of the footwear to thereby define the other portions of the side surface. COPYRIGHT: (C)2010,JPO&INPIT