Fibre-based transport packaging comes in two families. The multiwall kraft paper sack, filled to twenty or twenty-five kilograms and stacked in a keyed pattern, and the corrugated fibreboard case, filled to a smaller net weight and stacked in a column. Both are recyclable, both are cheap relative to their contents, and both fail in ways that surprise people who have only used one of them.
The choice is usually presented as a cost decision. It is more usefully treated as a decision about compression, humidity and handling count, with cost falling out of those three.
The short version
| Dimension | Multiwall kraft sack | Corrugated carton |
|---|---|---|
| Typical net weight | Higher, 20 to 25 kg | Lower, usually under 15 kg |
| Load bearing | The stack pattern carries the load | The box walls carry the load |
| Stack stability | Keyed pattern, deforms to fit | Column stack, needs alignment |
| Humidity tolerance | Poor without a barrier ply | Poor, compression strength falls sharply |
| Freezer suitability | Only with a barrier liner | Only with a barrier liner and a moisture-resistant board |
| Print quality | Limited | High, retail-ready |
| Handling | Manual, awkward, one at a time | Manual or automated, stackable, easier to count |
| Reclosure | None | Possible |
| Volume efficiency | High, conforms to product | Lower, fixed void |
How each one carries load
A corrugated case carries the stack load in its vertical walls. Its performance is described by edge crush resistance, which characterises the board, and by box compression strength, which characterises the finished case. The relationship between the two is not linear and depends on box dimensions, flute type and how the case is closed. A specification that names only the board grade has not specified the case.
A multiwall kraft sack carries almost nothing in itself. The stack is held by the pattern, by friction between plies and by the product settling. A well-keyed sack pallet is stable at heights that would crush a comparable carton stack, and a badly stacked one collapses on the first corner. This is why sack operations are more sensitive to palletiser discipline than carton operations.
Practical consequence: if pallets are stacked two or three high in a warehouse or in a truck, the carton has to be specified for the full compression load with a safety factor, and the sack has to be stacked in a defined pattern that is written down and audited.
Humidity is the decisive variable
Both materials lose strength as they take up moisture, and the loss is large. Corrugated fibreboard tested at standard conditioning conditions and the same board at high relative humidity are effectively different materials, with compression strength falling substantially as humidity rises. This is not a marginal derating; it is the reason carton stacks fail in cold stores and in humid ports rather than in the laboratory.
A cold store is a high humidity environment. So is a reefer container during defrost cycles, and so is any pallet moved from a freezer into a warm loading bay, where condensation forms directly on the outer surface. A carton specification derived from an ambient test and applied to frozen goods is a predictable failure.
Three mitigations are used. Moisture-resistant board grades and coatings raise the wet performance. A polyethylene inner liner keeps the product dry even if the outer softens, which is standard for frozen goods and is why the fibre outer in a freezer application is a secondary pack rather than a barrier. And stretch wrap transfers part of the stack load to the film and the pallet, which is the cheapest of the three and the most often relied on without being specified.
For dried goods stored at ambient, a humidity indicator card in the pallet and a desiccant where the product justifies it give early warning that the storage condition, not the packaging, is the problem.
Note the direction of the argument: a fluoro-free water-resistant coating is now the expected route, because Regulation (EU) 2025/40 restricts per- and polyfluoroalkyl substances in food contact packaging above defined thresholds. Where a supplier’s moisture-resistant board has historically relied on fluorinated chemistry, ask for written confirmation of the current position.
Handling, counting and labour
Handling count is an underrated cost. A pallet built from twenty-five kilogram sacks has around forty units; the same tonnage in ten kilogram cases has a hundred. Every unit is a manual handling event at filling, at palletising, at depalletising and at the customer. Where labour is the constraint, the sack wins on count and loses on ergonomics.
Cartons are easier to count, easier to label individually, easier to automate and easier to present. Where the outer will be opened at a retail back door or used for picking, the case is usually correct. Where the product goes into an industrial process and the outer is opened once by a machine or by an operator tipping it into a hopper, the sack usually is.
Labelling obligations attach to the pack the customer receives, and for a master carton or a sack that means lot identification, product identity and the particulars required by the applicable rules. The lot marking has to survive the environment: thermal transfer print on a coated surface behaves very differently from inkjet on unsealed kraft after a week at high humidity. The labelling requirements themselves are set out in the EU labelling guide.
What the packaging regulation adds
Regulation (EU) 2025/40 applies generally from August 2026 and brings two requirements that bear on this choice.
Packaging minimisation is the first. Grouped, transport and e-commerce packaging is subject to a limit on empty space, and packaging generally has to be reduced to the minimum necessary weight and volume for functionality and safety. A carton chosen for a fixed footprint and part-filled because it suits an old pallet pattern is exposed to this. A sack, which conforms to the product, generally is not. The person placing the packaging on the market has to hold documentation supporting the design choice, which means the compression calculation and the stack test are now compliance records rather than internal notes.
Design for recycling is the second. Fibre-based packaging is generally well placed here, but coatings, laminates and heavy ink coverage can move a pack down the recyclability performance grading. Ask a converter to state the grade it expects for the finished pack rather than for the base board.
Where wooden pallets cross a border, ISPM 15 applies to the pallet itself: wood packaging material must be treated and marked. That is a separate obligation from the fibre packaging, and it is a common cause of holds at entry.
Choosing between them
- Establish the storage and transit environment, in particular temperature and relative humidity, and whether the pallet crosses a temperature boundary.
- Establish stack height and duration, including any period in a warehouse rather than only in transit.
- Establish who opens the pack and how many times it is handled.
- If the environment is humid or frozen, assume a barrier liner is required regardless of the outer, and treat the fibre as a secondary pack.
- For a carton, specify box compression strength at the actual humidity with a stated safety factor, not the board grade alone.
- For a sack, specify the ply construction, the barrier ply and the stacking pattern, and audit the pattern.
- Run a real stack test, loaded, for a representative duration, at the real humidity.
- Check the empty space and minimisation position before committing a dimension.
The distribution of the two in practice reflects this. Cereals, groats and nut kernels in industrial volumes move in multiwall sacks. Frozen fruit and vegetables move in a polyethylene bag inside a carton, or in a bulk pack with a liner. Retail-facing goods move in cartons because the carton is the only one of the two that presents.
Where the comparison is usually got wrong
Testing at ambient and shipping at high humidity is the most common and most expensive error.
Specifying the board rather than the box is the second, because the finished case is what fails.
Relying on stretch wrap for compression without saying so is the third. If the film is carrying part of the load, that is a specification and it should be written and controlled, not assumed.
Treating the outer as a moisture barrier is the fourth. Neither kraft nor corrugated is a barrier; the liner is.
Vorezan’s position
Vorezan is an information platform. We do not sell packaging, test packaging or certify compliance, and nothing here is a specification recommendation for a particular product. Board performance, sack construction and coating chemistry vary by supplier, and regulatory positions change. Confirm the current text of Regulation (EU) 2025/40 and the applicable ISPM 15 requirements, and obtain product-specific test data and declarations from your supplier before committing a packaging specification.