Step 1: Melting the Resin
Raw plastic resin pellets are fed into an extruder, where a rotating screw pushes the material forward through a heated barrel. The heat and mechanical pressure melt the pellets into a thick, uniform molten plastic. For multi-layer film like POF, several extruders run in parallel, each melting a different resin layer that will later be combined.
Step 2: Forming the Film Bubble
The molten plastic is forced upward through a circular die, forming a continuous tube. Air is blown into the center of this tube, inflating it like a balloon -- this is where the process gets its name. As the bubble rises and expands, it stretches the plastic both around its circumference and along its length, which is what gives blown film its strength in multiple directions.
Step 3: Cooling and Flattening
As the bubble rises, an air ring cools the film so it solidifies at a consistent width and thickness. Once fully cooled, the bubble passes through collapsing frames that gradually flatten it into a double-layered sheet, which is then guided over rollers.
Step 4: Winding into Rolls
The flattened film is wound onto cores to form finished rolls, ready to be slit to the required width or sent on to printing and bag-making. Thickness is continuously monitored during this stage, since even small inconsistencies can affect how the film performs during heat shrinking or automated wrapping later on.
Why This Process Matters to Buyers
The quality of blown film extrusion directly affects how your finished packaging performs: uneven thickness can cause weak spots or inconsistent shrinkage, while poor cooling control can lead to cloudiness or wrinkling. When evaluating a film supplier, it is worth asking how many extrusion lines they run, how they monitor thickness consistency, and what quality checks are performed before film leaves the factory.
See the Process in Action
We run multiple blown-film extrusion lines producing PE and POF film daily, with in-line thickness monitoring on every run. If you would like to learn more about our production setup or request a sample to test film consistency yourself, visit our products page or get in touch with our team.
