A paper bag is already compostable before anyone adds anything to it. That is the part of the conversation that gets lost: the base sheet is not the problem, and the choice between kraft, greaseproof and parchment is a choice about strength and grease resistance rather than about disposal. What changes the outcome is what gets added afterwards — the coating or lamination that makes the bag hold oil or moisture, and the ink that makes it sell. This article looks at those two variables and what each one costs in compostability.
The base sheet is the easy part
Uncoated paper — kraft, white kraft, glassine, parchment — breaks down under composting conditions. A plain kraft bag with a plain water-based ink is close to a best case, and in most markets it can carry a compostability claim based on the paper.
What the base sheet does not do is hold back grease or liquid. That gap is what the coating exists to fill, and filling it is where the compostability claim starts to depend on something other than the paper.
The coating is where the claim is decided
Three options run through most of this market, and they are not equivalent:
- Polyethylene (PE) lamination. The classic grease and moisture barrier. It also makes the bag non-compostable, and it cannot be separated from the fibre in a composting process. A PE-lined bag is a plastic-lined bag with a paper outer.
- Water-based coating. Reaches grease hold-out without fluorochemistry and has certified compostable grades. It is the route to specify where the bag has to keep the claim — see water-based coated paper.
- Wax. Traditional, good moisture resistance and a clean feel, but it limits the temperature range, can transfer to the product, and is not a composting route in most specifications.
The pattern is consistent: the stronger the barrier, the more likely it is to be the layer that ends the claim. That is the trade to make explicit at the enquiry stage rather than after the customer has asked for the certificate.
Printing matters more than it looks
Ink coverage is the second variable and the one most often overlooked. A small logo in a water-based ink on a kraft bag is not the same specification as a full-coverage print in a conventional solvent ink. Full coverage means more ink, more of it in contact with the fibre, and — if the ink system is not chosen for it — more chance that the printed area behaves differently from the rest of the bag. Where the bag is meant to keep a compostability claim, specify the ink system at the same time as the coating, not afterwards.
Typical ranges — confirm against the actual batch. Kraft bags for food commonly run 40–120 gsm depending on load, with grease resistance and moisture-vapour transmission specified separately rather than as one barrier figure. Where a compostability claim is required, specify the standard and the disposal condition alongside the grammage.
By bag type: what to specify
| Bag and use | Barrier needed | Coating options | What is lost without it | Compostability |
|---|---|---|---|---|
| Bread and pastry | Low — mostly a light grease barrier | None, or a light water-based coat | Some grease marking on the outer | Holds without a coating |
| Fast food, fried items | High grease hold-out, short contact | Water-based grease coat | The bag marks through and softens | Holds if the coating grade is certified |
| Dried fruit and snacks | Moisture-vapour control | Water-based coat; PE where shelf life dominates | Product picks up moisture and loses crispness | Holds with a water-based coat; lost with PE |
| Produce | Low, plus wet strength | None; base sheet is chosen for wet strength | The bag tears when loaded wet | Holds |
| Gift and apparel | None | None; the finish is in the print and the handle | Nothing functional | Holds, unless a film laminate is used for gloss |
Common misuse
- Asking whether the bag is compostable instead of asking which coating it carries. The question cannot be answered without the second half.
- Specifying a PE-lined bag and a compostable base sheet together. The liner decides the outcome; the base sheet's properties do not transfer.
- Choosing the ink last. Full-coverage solvent print on a coated bag is a different specification from the sample that was tested.
FAQ
Are paper bags compostable by default?
Uncoated ones are, in the right conditions. Once a coating or lamination is added, the answer depends entirely on that layer, and a PE-lined bag is not compostable.
Does the bag need a grease barrier at all?
Only if the contents carry fat. Bread and produce need very little; fried food and pastry need it, and that is precisely the case where the coating choice decides the claim.
Can a printed bag still be compostable?
Yes, with an ink system chosen for it. Full-coverage conventional print is the case to check, because the ink load is highest there and the ink is not a composting material.
What should be specified on the enquiry?
The base sheet and grammage, the barrier the product needs, the coating route, the ink system and coverage, and — where a claim is required — the standard and the disposal condition it has to meet.
Browse the range
Start at eco paper bags for the range. Related base sheets: kraft paper bags, greaseproof paper bags and parchment paper bags.