A method of manufacturing a sole structure includes melting a first material in a first plasticization zone of a first injection line and melting a second material in a second plasticization zone of a second injection line. A first blowing agent is injected into the first material within a first mixing zone of the first injection line. The first blowing agent is a supercritical fluid within the first mixing zone. The first material and the second material are co-injected into a mold to form the sole structure. The first material is injected from a first injection chamber and the second material is injected from a second injection chamber. The first blowing agent nucleates within the mold to expand and foam the first material within the mold.