Abstract: A skeletal frame supporting a continuous sealed, flattened plastic film tube for retaining gas under positive pressure. The tube has opposed edges with a flexible film retainer line passing therethrough and extending beyond the end thereof to form edge beads. Guide strips having integral track means are positioned on opposite edges of the guide strip. The guide tracks receive and guide an edge of the flattened film tube drawn therethrough by the retainer line and retain the retainer line and film tube means in place on the skeletal structure. The plastic film tube of the fully assembled structure is a sealed envelope filled with a gas under positive pressure. In the preferred fully assembled wall structure, the plastic film has the form of a flattened four film layer forming two air-filled insulating layers. The film layer is formed from two concentric tubes, sealed at the ends to form a tubular sealed envelope, and the double walls are sealed to form a tubular envelope.