Two webs, two jobs
|
Selection point |
Forming film (bottom web) |
Lidding film (top web) |
|
What it does |
Stretched into the pocket shape |
Sealed flat on top of the formed pack |
|
Typical thickness in our supply range |
150–400 μm |
65–80 μm |
|
Key properties |
Formability, toughness, puncture resistance |
Sealing to the bottom web, appearance, printability |
Same structure, different gauge
We supply coextruded barrier films for both positions, including structures with PA, EVOH and PE layers. In our typical applications, the lid is often 65–80 μm and the bottom web is often 150–400 μm. The bottom web needs enough material to form the pocket, while the lid needs to seal reliably to it.
Why the same structure name does not make films interchangeable
A film specified as a lid has not automatically been selected for the required draw. Equally, a bottom web may add unnecessary material or handle poorly when used as a lid. Check the intended use, sealing surface and machine requirements before considering a substitution.
The two webs must work together
Seal layers must be compatible. The lid needs to seal to the inner surface of the bottom web under the intended machine conditions. For boiling or retort packs, both webs and the finished seal need to suit the heat treatment.
Consider the barrier of the complete pack. Oxygen can enter through either web, so choosing a high-barrier bottom film alone may not meet the product requirement. The lid and bottom web do not need identical constructions, but their combined performance needs to suit the intended shelf life.
Lidding film options
Lidding films can be coextruded or laminated, and they can be printed. See our laminated top film for thermoforming packs.
Selecting the two webs for a trial
Send us the product, approximate pocket depth, storage and heat treatment conditions, and whether the lid is printed. Existing lid and bottom-web specifications are helpful if available. We can recommend sample options for testing together on your line. Use the trial to confirm forming, seal integrity and the opening behaviour you need before final selection. Explore our thermoforming films.
