BOPP is produced by stretching polypropylene film in both the machine direction and cross direction after extrusion, a process called biaxial orientation. That stretching realigns the polymer chains and produces a film with outstanding clarity, high gloss, and significant stiffness, well beyond what unoriented polypropylene or polyethylene can achieve at comparable gauge.
The orientation process that gives BOPP its strength and clarity also makes it a poor sealant on its own, since the same molecular alignment that creates stiffness resists forming a strong heat seal. BOPP is almost always laminated or coextruded with a sealable layer, such as CPP, and used primarily as the outer print and barrier layer in a structure rather than as the seal-contact surface. It is a workhorse for label stock, snack food overwrap, and any application where shelf appeal and print quality drive the specification.