A sole structure for an article of footwear , the sole structure comprising: a fluid-filled chamber including a barrier formed from a polymer material, the barrier forming an exterior of the fluid-filled chamber and defining an interior cavity that contains a pressurized fluid, the barrier comprising a first barrier portion , an opposite second barrier portion and a sidewall barrier portion , the sidewall barrier portion (i) extending around a periphery of the chamber , (ii) being formed by the second barrier portion , and (iii) being joined to the first barrier portion at a peripheral bond located around an upper portion of the fluid-filled chamber at an end of the sidewall barrier portion ; and a tether element disposed within the interior cavity and including an upper plate secured to an inner surface of the first barrier portion , an opposite lower plate secured to an inner surface of the second barrier portion , and a plurality of tethers extending between and secured to the upper plate and the lower plate , the plurality of tethers spacing the upper plate and the lower plate apart from each other, the upper plate being contoured to have a non-planar configuration, wherein the contour of the upper plate forms a depression in a central area of the upper plate , wherein the central area is centrally located between a medial side of the sole structure and a lateral side of the sole structure , characterized in that a stiffness of the upper plate is greater than a stiffness of the material forming the first barrier portion and the second barrier portion ; and a stiffness of the lower plate is greater than a stiffness of the material forming the first barrier portion and the second barrier portion . a fluid-filled chamber including a barrier formed from a polymer material, the barrier forming an exterior of the fluid-filled chamber and defining an interior cavity that contains a pressurized fluid, the barrier comprising a first barrier portion , an opposite second barrier portion and a sidewall barrier portion , the sidewall barrier portion (i) extending around a periphery of the chamber , (ii) being formed by the second barrier portion , and (iii) being joined to the first barrier portion at a peripheral bond located around an upper portion of the fluid-filled chamber at an end of the sidewall barrier portion ; and a tether element disposed within the interior cavity and including an upper plate secured to an inner surface of the first barrier portion , an opposite lower plate secured to an inner surface of the second barrier portion , and a plurality of tethers extending between and secured to the upper plate and the lower plate , the plurality of tethers spacing the upper plate and the lower plate apart from each other, the upper plate being contoured to have a non-planar configuration, wherein the contour of the upper plate forms a depression in a central area of the upper plate , wherein the central area is centrally located between a medial side of the sole structure and a lateral side of the sole structure , characterized in that a stiffness of the upper plate is greater than a stiffness of the material forming the first barrier portion and the second barrier portion ; and a stiffness of the lower plate is greater than a stiffness of the material forming the first barrier portion and the second barrier portion . <EOS>