What is the difference between blown film and cast film?

Blown film extrusion pushes molten resin through a circular die and inflates it with air into a bubble, which is then cooled, collapsed, and wound into rolls. Because the bubble expands and stretches the film in multiple directions during cooling, blown film tends to have more balanced mechanical properties in both the machine direction and the cross direction, which is a major reason it dominates bag, liner, and general packaging film.

Cast film is extruded through a flat die directly onto a chilled roller, which freezes the film almost instantly. That fast, controlled cooling produces higher clarity, higher gloss, and a more consistent gauge profile, but the film is more oriented in the machine direction, meaning its strength is less balanced between directions than blown film.

The right process depends on the priority. If you need balanced strength, gusseting, or a wide range of structures including barrier layers, blown film is usually the better fit. If you need maximum clarity and gloss for something like a stand-up pouch face film, cast film has the edge.