The Dystor® system includes two durable membranes. The outer is cable restrained and remains inflated in a fixed position. The inner membrane moves freely as it stores or releases gas generated from the anaerobic digestion process. A preset operating pressure is continuously maintained between the two membranes. This system can hold up to three times as much gas as conventional digester covers and consequently maximizes the energy benefits of the process, as well as, the cost savings.