BOPP laminated polypropylene is the acronym for biaxially oriented polypropylene (outside) over polypropylene (woven interior), a petroleum byproduct. It refers to the combination of woven polypropylene used to construct the bags and an additional layer, or laminated surface, of polypropylene, on which graphic images are printed. In constructing the bags, the raw polypropylene material is first extruded, then slit into individual strands, then wound like yarn. The yarn-like material is placed on a knitting machine, which weaves the fabric used to make the bags. Extruded polypropylene is a very strong material, but when woven, its structural integrity is dramatically enhanced, providing the superior product protection on which BOPP/PP bags have built their reputation.