Cast film vs blown film
The difference between cast and blown film
It is the difference in extraction that gives the wrap different attributes.
This is the traditional way of producing film and takes its name from the process used to create it. Heated resin is blown through a circular die, and a thick layer of extruded film emerges as a large bubble. The bubble can be many feet tall – and it is this height that allows the film to gradually cool before rollers collapse the bubble and flatten the material for shaping onto rolls.
The very nature of blown film makes it a pre-stretched product, and the thickness of blown film is adjustable dependent on the diameter of the tube from which it comes.
Cast film is created by feeding a sheet of heated resin through a flat die. The molten material emerges from the die and out onto larger chilling rollers which cool and solidify the material. It is then ready for trimming and rolling.
Cast film is minimally pre-stretched compared with blown film giving it improved depth of drawing for thermoforming operations. The cooling process can be used to produce different characteristics in the final product. Cast film can be thinned by winding the film out of the roller faster than it is extruded.
When to use cast film, and when to use blown film
There are likely to be many factors to consider when choosing which film to use. These may include the environmental conditions (is it cold or frozen?) storage and transportation processes, and what level of pre-stretch is needed. Here is a quick breakdown of the pros and cons of each type of film.
- Has a higher resistance to puncture; preferred for wrapping sharp-edged products and heavy loads such as masonry and construction materials
- Film offers less clarity due to crystallisation which occurs during manufacture
- Has a high level of cling
- Comes off the roll easily and is quieter than blown film
- Often used for lighter products, and loads stacked on pallets
- Very clear product making it easy to scan barcodes through the film
- Requires less force to stretch
- High tear resistance
What else should you consider?
With all this said, how do you work out which film is best for your requirements?
While both blown and cast film offer excellent pre-stretch performance and effective load containment, the shift in the market towards cast film is with good reason. Not only does cast film deliver excellent environmental performance through its high yield, but it also provides greater clarity and quiet unwind is making it an increasingly popular choice.
Not coincidentally, NanoWrap provides the highest standard in modern cast film for packaging pallets. It is ultra-thin, incredibly light and extraordinarily strong – stronger than the competition. Our 33-layer cast film continually delivers a far greater performance compared with the 5-7 layer blown film of yesterday.
Talk to us. We’re always ready to help you work out which film will work best for your requirements.