An inflatable building is a structure constructed using two layers of membrane connected together, typically using spars made from the same material. The cavity formed between the layers is pressurized with air producing a rigid structural element which allows large span structures to be achieved. The key difference between air-supported buildings and inflatable buildings is that air-supported buildings require airlocks at all the access points to prevent air being lost when doors are opened since the entire occupied space of the building is pressurized.