The main body of the bag consists of woven polypropylene (PP) flat-yarn fabric and imported Canadian white kraft paper or Russian yellow kraft paper. The plastic layer is formed via the casting of PP granules. In addition to polypropylene (PP), the plastic layer may also utilize woven flat-yarn fabric based on polyethylene (PE) as its substrate. The kraft paper component consists of specialized, refined composite-grade paper, featuring a basis weight of 25–80 g/m² and a moisture content of ≤0.4%. In accordance with the requirements of standard GB8946-2013, the composite bonding strength is ≥3.0 N/15 mm. Common structural configurations include:
Two-in-One Type: A single layer of woven fabric laminated with refined kraft paper.
Three-in-One Type: Woven fabric + coating layer (PP film) + kraft paper. When an additional inner liner bag is included, a four-layer composite structure is formed, enhancing moisture resistance and sealing performance to achieve a moisture vapor transmission rate of <5 g/m²·24h.
Paper-plastic composite bags may be further classified as follows: By primary material-into polypropylene "two-in-one" bags, polypropylene "three-in-one" bags, polyethylene "two-in-one" bags, and polyethylene "three-in-one" bags; By sewing method-into bottom-sewn bags, side-and-bottom-sewn bags, valve bags, and bonded-sewn bags; and By effective bag width-into 450 mm, 500 mm, 550 mm, 600 mm, 650 mm, and 700 mm sizes.
