This invention relates to a hollow profile (1) used for the manufacture of a spirally wound double-walled thermoplastic pipe, which hollow profile has essentially a rectangular cross section and the wall (2) of the hollow profile intended to form the inner wall of the pipe is thicker than the wall (4) intended to form the outer wall (4) of the pipe. The invention is characterized in that the inner rounding radius (7a) of the edges adjacent to the thicker wall (2) of the hollow profile is considerably larger than the rounding radius (7) of the two other edges of the cavity (6).