Pork bellies are the underside of the hog, from which bacon is made. Pork bellies and pork belly futures contracts are traded on the Chicago Mercantile Exchange. Pork bellies can be kept in cold storage for an extended period of time, and generally it is the frozen bellies that are most actively traded. Bellies typically weigh around 13 pounds. Prices vary depending on the amount of inventory in cold storage and the seasonal demand for bacon.