Abstract: Insulated string segment contains an inner pipe with reinforcements on its ends, centrators located on it, insulation and gas absorbers, outer pipe with external thread on its ends and connecting coupling. Outer pipe is produced with pressure isolated valve providing creation of 10?4-10?3 mm of Mercury vacuum in the interpipe space. Steel insertions made in a form of spools and welded to inner and outer pipes with vacuum-tight seams are located in the interpipe space so as to provide groove produced on the insertion and an outer pipe create hollow. Centrators are made in a form of clamps with two parts closely tightened to each other with inner surface made with friction properties. The string is useful in oil and gas extraction for forcing the heat-transfer agent into a layer. Reduction of heat loss during passage through the string and improvement of service ability of the string are provided.