The present invention relates to a method of producing flexible polypropylene woven sacks with heat-fused seams comprising providing fabric pieces, wherein each piece of fabric has a coated side and an uncoated side; positioning pieces of fabric so that a coated side of one piece of fabric is face-to-face with a coated side of another piece of fabric; selecting an area of fabric to be joined to form a seam or joint; applying heat to the area to be joined that is less than the melting point of the tissues,