Insertion sheet between high-temperature duct and structural member of aircraft, duct of aircraft, and aircraft

Temperature of a structural member is maintained at allowable temperature or less by suppressing heat transfer from a high-temperature duct to the structural member. An insertion sheet according to the present invention is inserted between a flange and a partition panel. The flange is provided on a bleed duct and is fastened to the partition panel. The bleed duct penetrates through a partition wall of an aircraft. The insertion sheet includes first parts and a second part. The first parts are disposed near respective shafts of rivets provided at a plurality of positions of the insertion sheet. The second part extends among the first parts. The first parts bear a load of fastening, and the second part has thermal conductivity lower than thermal conductivity of the first parts.