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- Coefficient of friction (COF)
Coefficient of friction (COF)
Also known as: coefficient of friction, COF, slip, static COF, kinetic COF, film slip properties
Coefficient of friction (COF) shows how easily a film surface slides over another surface; it is critical for automatic packing machines.
The coefficient of friction (COF) is a dimensionless number describing how much a film resists sliding over another surface. Lower values mean a more slippery film. It is one of the most important specifications for rollstock running on automatic packing lines.
Static and kinetic
Static COF is the resistance to start moving; kinetic COF is the resistance while moving. Both are measured to standard methods by pulling a weighted sled across the film, and can be measured film-to-film or film-to-metal, inside or outside face.
Why it matters
On VFFS and HFFS machines, film slides over rollers, a forming shoulder and a tube. If COF is too high, film drags, wrinkles or breaks; if too low, pull belts slip and registration drifts. Premade pouches also need suitable COF to stack, feed and palletise well.
Controlling COF
Slip and antiblock additives are used, but slip additives migrate over time, so COF can change after production. Temperature, lacquers and lamination also affect it. There is no universal ideal value: share your machine model, speed and any recommended COF range with your converter, and run a trial on your line when changing structures.
Frequently asked
What is a good COF for packaging film?
It depends on the machine and application; many lines specify a target range, so ask your machine supplier and converter.
Why does COF matter for premade pouches?
It affects how pouches stack, slide in cartons, and feed into automatic opening and filling machines.
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