The dual layer membrane design has a flexible PVC lined poly outer layer and an inner polyethylene bladder layer. The outer provides weather protection while the inner provides gas storage volume. The air between the inner and outer layers act as an insulating barrier against heat loss, maintains a fully inflated outer layer and keeps constant pressure on the gas bladder. Below both roof layers is a strap and netting structure. This offers support for the roof and provides surface area for sulfur build up during the biogas desulphurization process. The roof layers are fastened to the tank using a stainless steel channel and an inflation tube. This is the most popular method for fastening membranes as it offers superior safety characteristics over the bolt down roof systems.