a method of producing a rectangular cross - section cardboard tubing by passing a plurality of cardboard strips having a thermoplastic coating thereon through a heating unit so as to hear the plurality of strips and melt the thermoplastic coating . thereafter , the plurality of heated strips are passed through a guiding unit so as to align the strips in an overlapped configuration . the aligned plurality of strips are wound around an elongated , rectangular cross - section , rotating core so as to place the plurality of strips in an overlapped , spiral configuration along the core and form a tubing . the tubing is fed along the core , and a cutting unit cuts the tubing into lengths .