Method for manufacturing a thermally insulated flexible tube consisting of a working tube, a layer of thermal insulation and an outer protective tubular casing, including the following: first the outer protective tubular casing is extruded coaxially to the working tube by means of an extrusion head with an angular flow of the melt of polymeric materials, and thereafter a foaming material is fed into the inner cavity between the outer protective tubular casing and the working tube, said foaming material forming a layer of thermal insulation between the outer protective tubular casing and the working tube, wherein the method is realized using a production line of the thermally insulated flexible tube which production line comprises the following elements: - an unwinding device for supplying the working tube, - a straightening device with a pre-heating system, - a guiding device for positioning the working tube, - a high-precision filling unit arranged adjacent to the extrusion head, - an extruder, - a rotating calibrating device, placed in a cooling tub, - a pulling device, - a cutting device and - a winding device for the finished thermally insulated flexible tube, wherein the outer protective tubular casing is manufactured with a helical surface by means of the rotating calibrating device and is thermally stabilized in the cooling tub, subsequently the foaming thermally insulating material for forming the layer of thermal insulation is fed into the thermally stabilised cavity between the working tube and the helical surface of the outer protective tubular casing with the aid of the high-precision filling unit, while the temperature of the foaming thermally insulating material supplied is maintained by means of a conditioning system which cools the channels of the device for feeding and mixing the foaming thermally insulating materials and at the same time acts as an element for the positioning of said channels, wherein the conditioning system is arranged in a cavity between the working tube and the helical wall of the outer protective tubular casing, wherein a coil of the conditioning system cools the feeding channel for the foaming thermally insulating material and also a space around the coil. first the outer protective tubular casing is extruded coaxially to the working tube by means of an extrusion head with an angular flow of the melt of polymeric materials, and thereafter a foaming material is fed into the inner cavity between the outer protective tubular casing and the working tube, said foaming material forming a layer of thermal insulation between the outer protective tubular casing and the working tube, wherein the method is realized using a production line of the thermally insulated flexible tube which production line comprises the following elements: - an unwinding device for supplying the working tube, - a straightening device with a pre-heating system, - a guiding device for positioning the working tube, - a high-precision filling unit arranged adjacent to the extrusion head, - an extruder, - a rotating calibrating device, placed in a cooling tub, - a pulling device, - a cutting device and - a winding device for the finished thermally insulated flexible tube, - an unwinding device for supplying the working tube, - a straightening device with a pre-heating system, - a guiding device for positioning the working tube, - a high-precision filling unit arranged adjacent to the extrusion head, - an extruder, - a rotating calibrating device, placed in a cooling tub, - a pulling device, - a cutting device and - a winding device for the finished thermally insulated flexible tube, wherein the outer protective tubular casing is manufactured with a helical surface by means of the rotating calibrating device and is thermally stabilized in the cooling tub, subsequently the foaming thermally insulating material for forming the layer of thermal insulation is fed into the thermally stabilised cavity between the working tube and the helical surface of the outer protective tubular casing with the aid of the high-precision filling unit, while the temperature of the foaming thermally insulating material supplied is maintained by means of a conditioning system which cools the channels of the device for feeding and mixing the foaming thermally insulating materials and at the same time acts as an element for the positioning of said channels, wherein the conditioning system is arranged in a cavity between the working tube and the helical wall of the outer protective tubular casing, wherein a coil of the conditioning system cools the feeding channel for the foaming thermally insulating material and also a space around the coil.