A thermally insulated duct element , for transporting air, in particular for making an air transport network in a building air management and distribution system, said thermally insulated duct element comprising: - a rigid inner tube that includes an inner surface , an outer surface and two ends that are each ended by an end edge , - a rigid outer tube that includes an inner surface , an outer surface and two ends that are each ended by an end edge , said outer tube being concentric to said inner tube , held separate from the latter by at least two annular spacer systems that are arranged at the ends of said inner tube and said outer tube , between the opposite surfaces of said inner tube and said outer tube , said annular spacer systems being made of a thermally insulating material and defining between each other at least one section of annular space suitable for containing air or an insert of thermally insulating material, characterized in that it comprises at least one insert tube (7; 7a, 7b) arranged concentrically between said inner tube and said outer tube , separated from these latter by said two annular spacer systems that are arranged at the ends of said inner , outer and insert (7; 7a, 7b) tubes, to create a plurality of annular spaces superimposed between said inner tube and said outer tube , each annular spacer system that is arranged at one end of said inner , outer and insert tubes being consisted of a single-piece tip (4a3, 4a4, 4a5): - a tubular inner surface of which is in contact with the outer surface of the inner tube , - a tubular peripheral surface of which is in contact with the inner surface of the outer tube , and - that comprises an internal housing for receiving one end of each insert tube . said thermally insulated duct element comprising: - a rigid inner tube that includes an inner surface , an outer surface and two ends that are each ended by an end edge , - a rigid outer tube that includes an inner surface , an outer surface and two ends that are each ended by an end edge , - a rigid inner tube that includes an inner surface , an outer surface and two ends that are each ended by an end edge , - a rigid outer tube that includes an inner surface , an outer surface and two ends that are each ended by an end edge , said outer tube being concentric to said inner tube , held separate from the latter by at least two annular spacer systems that are arranged at the ends of said inner tube and said outer tube , between the opposite surfaces of said inner tube and said outer tube , said annular spacer systems being made of a thermally insulating material and defining between each other at least one section of annular space suitable for containing air or an insert of thermally insulating material, characterized in that it comprises at least one insert tube (7; 7a, 7b) arranged concentrically between said inner tube and said outer tube , separated from these latter by said two annular spacer systems that are arranged at the ends of said inner , outer and insert (7; 7a, 7b) tubes, to create a plurality of annular spaces superimposed between said inner tube and said outer tube , each annular spacer system that is arranged at one end of said inner , outer and insert tubes being consisted of a single-piece tip (4a3, 4a4, 4a5): - a tubular inner surface of which is in contact with the outer surface of the inner tube , - a tubular peripheral surface of which is in contact with the inner surface of the outer tube , and - that comprises an internal housing for receiving one end of each insert tube . - a tubular inner surface of which is in contact with the outer surface of the inner tube , - a tubular peripheral surface of which is in contact with the inner surface of the outer tube , and - that comprises an internal housing for receiving one end of each insert tube . <EOS>