A sole structure for an article of footwear comprising: a midsole (118; 218) having four stacked polymeric sheets bonded to one another to define a first sealed chamber bounded by a first polymeric sheet and a second polymeric sheet, a second sealed chamber bounded by the second polymeric sheet and a third polymeric sheet, and a third sealed chamber bounded by the third polymeric sheet and a fourth polymeric sheet; wherein the second polymeric sheet and the third polymeric sheet are bonded to one another between the first sealed chamber and the third sealed chamber at bonds at least some of which have an outer periphery with a closed shape and with the second sealed chamber bordering the outer periphery; wherein the first sealed chamber and the second sealed chamber are disposed adjacent to a ground-facing surface of the midsole (118; 218); an outsole secured to the ground-facing surface of the midsole (118; 218); wherein the outsole has relatively thick portions under the first sealed chamber and relatively thin portions under the second sealed chamber such that, under a first compressive load, only the relatively thick portions form a ground contact surface, and under a second compressive load greater than the first compressive load, the first sealed chamber compresses such that both the relatively thick portions and the relatively thin portions form the ground contact surface; wherein the first sealed chamber and the second sealed chamber include a plurality of tubular sub-chambers extending lengthwise at least partially transversely across the midsole (118; 218) at the ground-facing surface; wherein a first of the tubular sub-chambers of the second sealed chamber extends at a first acute angle to a longitudinal midline of the midsole (118; 218) from a medial edge of the midsole (118; 218) to a lateral edge of the midsole (118; 218) uninterrupted by the first sealed chamber and the third sealed chamber, establishing a first flexion axis about which the midsole (118; 218) flexes; a second of the tubular sub-chambers of the second sealed chamber extends at a second acute angle to the longitudinal midline of the midsole (118; 218) from the medial edge of the midsole (118; 218) to the lateral edge of the midsole (118; 218) uninterrupted by the first sealed chamber and the third sealed chamber, establishing a second flexion axis about which the midsole (118; 218) flexes; and the first flexion axis and the second flexion axis intersect in a forefoot region of the midsole (118; 218). a midsole (118; 218) having four stacked polymeric sheets bonded to one another to define a first sealed chamber bounded by a first polymeric sheet and a second polymeric sheet, a second sealed chamber bounded by the second polymeric sheet and a third polymeric sheet, and a third sealed chamber bounded by the third polymeric sheet and a fourth polymeric sheet; wherein the second polymeric sheet and the third polymeric sheet are bonded to one another between the first sealed chamber and the third sealed chamber at bonds at least some of which have an outer periphery with a closed shape and with the second sealed chamber bordering the outer periphery; wherein the first sealed chamber and the second sealed chamber are disposed adjacent to a ground-facing surface of the midsole (118; 218); an outsole secured to the ground-facing surface of the midsole (118; 218); wherein the outsole has relatively thick portions under the first sealed chamber and relatively thin portions under the second sealed chamber such that, under a first compressive load, only the relatively thick portions form a ground contact surface, and under a second compressive load greater than the first compressive load, the first sealed chamber compresses such that both the relatively thick portions and the relatively thin portions form the ground contact surface; wherein the first sealed chamber and the second sealed chamber include a plurality of tubular sub-chambers extending lengthwise at least partially transversely across the midsole (118; 218) at the ground-facing surface; wherein a first of the tubular sub-chambers of the second sealed chamber extends at a first acute angle to a longitudinal midline of the midsole (118; 218) from a medial edge of the midsole (118; 218) to a lateral edge of the midsole (118; 218) uninterrupted by the first sealed chamber and the third sealed chamber, establishing a first flexion axis about which the midsole (118; 218) flexes; a second of the tubular sub-chambers of the second sealed chamber extends at a second acute angle to the longitudinal midline of the midsole (118; 218) from the medial edge of the midsole (118; 218) to the lateral edge of the midsole (118; 218) uninterrupted by the first sealed chamber and the third sealed chamber, establishing a second flexion axis about which the midsole (118; 218) flexes; and the first flexion axis and the second flexion axis intersect in a forefoot region of the midsole (118; 218).