An article of footwear may have an upper and a sole structure secured to
the upper. The sole structure includes a fluid-filled chamber with a
first surface, an opposite second surface, and a third surface extending
between the first and second surfaces. Whereas the first surface and the
second surface each have a thickness of one sheet of a polymer material,
the third surface has a thickness of two overlapping sheets of the
polymer material. The third surface may be exposed to an exterior of the
footwear to form a portion of a side surface of the sole structure.