Blown vs. Cast - How is stretch film made?
January 07, 2020
There's no single "best" film
Every application and company is different. Sure, there are commonalities, but there's a lot of detail that film experts and local reps consider when suggesting the optimal stretch film for an application. The "best stretch film" is relative - based on your goals, circumstances and expectations.
Blown stretch film
Film gauge, pre-stretch capability, puncture resistance, tear propagation and other performance characteristics are examples of the specs which the film experts will consider with you as they help to select a film.
There's a basic difference in how films are manufactured though that's interesting to understand as someone who relies on the "system" of stretch wrapping equipment and film to safely deliver your loads to their destination.
Films are either blown or cast.
Let's look at the difference in the manufacturing process. Please note - this is intended to be informative and not to specify one method or material or another.
Cast stretch film
Cast film production involves a different process. In this case the resin is extruded through a linear die and oozes out onto large diameter chilling rollers. (Note that they may not actually be cold, but rather are much cooler than the semi-molten plastic.) Depending on the original thickness of extrusion, sometimes film is thinned to the target gauge by winding the resulting film faster than it is extruded.
This is a horizontal process as shown in the schematic.
Cast film represents the other 70-80% of stretch film manufacturing according to general industry estimates.
