What changes on a filling line when you switch to compostable pouches?
Three things change: seal temperature, film stiffness and shelf life. Compostable PLA and PBAT films generally seal at a lower temperature than the PE film they replace, so an existing seal setting usually scorches them. The film is also less stiff, so it can track badly on a former set up for PE. Both are fixed by trial, not by specification.
Last checked against the live site: 2026-11-04
The failure mode in most compostable switches is not the material. It is that the line was set up for polyethylene, and the seal bars, the forming shoulder and the gas flush are all still tuned for polyethylene. This page sets out what actually changes, in the order it usually bites.
Seal temperature comes first
Polylactic acid and polybutylene adipate terephthalate blends have a lower seal initiation temperature than the low density polyethylene they typically replace. A sealing jaw set for PE will often overheat the compostable film, producing a seal that looks closed but has a weak, brittle weld that fails under fill weight or in transit.
The fix is a temperature ladder rather than a single setting: run a strip at increasing jaw temperature and increasing dwell, then pull each seal by hand and record where it peels cleanly rather than tearing. That gives you a working window, and the window is usually narrower than for PE, which is the part people underestimate.
Cold seal exists for some compostable structures and removes the heat problem entirely, but it constrains the design and is not available on every construction.
Film stiffness and machine tracking
Compostable film is generally softer and more extensible than PE at the same gauge. On a vertical form fill seal machine that means it can wander on the forming shoulder, produce inconsistent lap seals, and wrinkle where a stiffer film would have tracked straight.
Two adjustments usually recover it: slightly higher film tension, and a slower fill cycle during the trial. Neither is a permanent fix if the machine was specified around a stiff film, which is why a trial roll matters more than a data sheet.
On a horizontal line the symptom is different: the film can stretch during indexing, which shows up as print that drifts out of register along the run rather than across it.
Barrier and shelf life
Compostable films are generally poorer oxygen and moisture barriers than the metallised or foil laminates they replace. For coffee, nuts, dried fruit and anything fat-sensitive, that shows up as a shorter shelf life at the same pack format.
There are two honest responses. Shorten the stated best-before and say so, or add a high-barrier layer, which reintroduces a non-compostable component and removes the compostable claim. There is no third option at commercial cost today.
This is the point at which many brands discover that the packaging change is really a product change, and it is worth knowing before the artwork is approved rather than after.
The trial sequence that actually de-risks it
- 1Get a sample kit and seal it on your own machine
Not on ours. The seal jaw geometry, the dwell time and the fill weight are all yours, and a seal that passes on a lab sealer can fail on a production jaw.
- 2Build a temperature ladder before touching production settings
Run strips at increasing jaw temperature and dwell, pull each one by hand, and record where the seal peels cleanly instead of tearing or delaminating. You are looking for a window, not a number.
- 3Run 50 to 100 units at reduced speed
Watch tracking on the forming shoulder and register drift along the run. Adjust film tension first, then cycle speed. Do not adjust both at once or you will not know which one worked.
- 4Store the trial packs for the full stated shelf life
Barrier differences only show up over weeks. Keep one pack at ambient and one at elevated temperature, and open them on a schedule.
- 5Only then approve artwork
Artwork approval locks the film construction. Approving before the seal and shelf life trials are complete is how brands end up with a pallet that will not run.
Where the honest answer is no
Stated up front rather than discovered after the order.
- !A compostable film will not match a metallised or foil laminate on oxygen barrier. If the product needs 12 months of shelf life, the compostable claim and the shelf life are in direct conflict.
- !Retort and vacuum processes exceed what current compostable films survive. Recyclable mono-PE or mono-PP is the realistic route, not compostable.
- !The seal window for compostable film is usually narrower than for PE. A line that runs at the edge of its tolerance on PE may not run at all on compostable without mechanical changes.
- !Certification covers the film. Changing the ink, the adhesive or the closure means the certified construction is no longer the one you are running.
Frequently asked
Do I need a new sealing machine for compostable pouches?+
Usually not, but you do need a new temperature setting and a trial. Compostable PLA and PBAT films generally seal at a lower jaw temperature than PE, so a setting carried over from PE tends to scorch the film and produce a weak weld.
Why does compostable film track badly on my machine?+
It is softer and more extensible than PE at the same gauge, so it can wander on a forming shoulder set up for a stiffer film. Higher film tension and a slower cycle during the trial usually recover it.
Will shelf life drop if I switch to compostable packaging?+
Often, yes, if you are replacing a metallised or foil laminate. Compostable films generally have lower oxygen and moisture barrier. You either shorten the stated best-before or add a barrier layer, which removes the compostable claim.
Can I test before committing to a production run?+
Yes. The $40 sample kit ships in 48 hours, contains several shapes and materials, and the full amount comes off your first production order. Seal it on your own machine rather than a lab sealer.
Does changing the ink affect the certification?+
Yes. Certificates cover the film construction. The ink, adhesive and closure have to be confirmed separately, so a certified film with an uncertified ink is not a certified pack.