A double-walled tube section for constructing a double-walled tube segment suitable for underpressure applications such as an evacuated tube transport system including elongated curved outer shell parts, interlayer shell parts and an inner wall. The elongated curved outer shell parts form the outer wall of the double-walled tube segment. The interlayer shell parts are of thin sheet and include a rectanqular portion having short edges and long edges and a flange on at least one of the short edges.