Sole assembly with plural portions that cooperatively define chamber

A method of manufacturing a sole assembly for an article of footwear that includes an interior space that receives a foot of a wearer, the article of footwear also including an exterior surface, the method comprising:

• molding a first portion of the sole assembly, the first portion including a first surface that at least partially defines the interior space, the first portion also including a first chamber surface that opposes the first surface, the first portion also including a first rail member that projects from the first chamber surface;
• molding a second portion of the sole assembly, the second portion including a second surface that at least partially defines the exterior surface of the article of footwear, the second portion also including a second chamber surface that opposes the second surface, the second portion also including a second rail member that projects from the second chamber surface;
• compressing and molding the first portion to the second portion such that the first chamber surface and the second chamber surface cooperate to at least partially define a substantially sealed chamber within the sole assembly and such that the first rail member attaches to the second rail member;
• and
• changing a pressure inside the chamber via a valve included in the first portion,
• wherein molding the first portion and molding the second portion includes molding the first portion and the second portion together within a single mold assembly,
• wherein the mold assembly includes a first mold member, a middle mold member, and a second mold member, wherein molding both the first portion and the second portion together includes molding the first portion between the first mold member and the middle mold member and molding the second portion between the middle mold member and the second mold member, and further comprising removing the middle mold member from between the first portion and the second portion and subsequently securing the first portion to the second portion by moving at least one of the first mold member and the second mold member toward the other, and
• wherein the first portion is made of a different material from the second portion.