A cushion comprised of at least one chamber comprised of a barrier material, said barrier material comprised of an elastomer, said elastomer being at least semi-permeable to at least a first reactant compound, a second reactant compound disposed within said at least one chamber, wherein said first reactant compound and said second reactant compound react to form a resultant compound, and wherein a rate of diffusion of said resultant compound through said barrier material is less than a rate of diffusion of said first reactant compound through said barrier material. An article of footwear including a cushion, said cushion comprised of at least one chamber comprised of a barrier material, at least a first and a second solid or liquid reactant compounds disposed within said at least one chamber, wherein said first reactant compound and said second reactant compound react to form a resultant gaseous compound.