Both grades are corrugated containers. Both arrive baled, both look much the same on a photograph, and both are quoted per metric ton. The difference is what has been taken out before baling, and that difference is written into the specification as two numbers.
What the specification actually says
Under ISRI PS-2013, grade 11 is corrugated containers having liners of either test liner or kraft. That is the whole definition. It does not restrict where the material came from or what else may have travelled with it, beyond the tolerance limits.
Grade 12 is narrower. It is double-sorted corrugated, generated from supermarket, industrial or commercial sources, and the material has been specially sorted to be free of boxboard, off-shore corrugated, plastic and wax. Those four exclusions are the substance of the grade. Everything else follows from them.
| Grade | ISRI No. | Prohibitives | Outthrows + prohibitives |
|---|---|---|---|
| OCC | #11 | 1% | 5% |
| DSOCC | #12 | 0.5% | 2% |
Tolerances as published in ISRI PS-2013 for each grade. Tighter limits can be agreed in writing before booking; looser ones cannot, because at that point the lot is no longer the grade.
Why two numbers, and not one
The pairing confuses people who are new to the trade, and it is worth separating because the two limits fail in different ways.
Outthrows are papers unsuitable for the grade as packed — the wrong stock in the right bale. They reduce the yield of the lot. The mill still runs it; it simply gets less usable fibre per ton than the invoice implies.
Prohibitive materials are different in kind, not degree. They are things that risk damaging equipment, or that make the packed lot unusable as the grade. Wax-coated board is the textbook case in corrugated: it does not repulp, it contaminates the furnish, and it is not a yield question but a rejection question.
The same material can be an outthrow in one grade and a prohibitive in another.
This is why the grade number, not the description, is what gets contracted. "Clean OCC" means nothing enforceable. "#12 DSOCC" carries both limits with it, and both are testable at the discharge port.
What double-sorting is actually buying
Going from 1% to 0.5% on prohibitives, and from 5% to 2% on the combined figure, costs real labour at the sorting line. A buyer paying the premium for grade 12 is buying three things:
- Yield. Less of each ton is removed before the fibre reaches the pulper.
- Strength consistency. Excluding boxboard and off-shore corrugated narrows the range of liners and fluting in the furnish, which makes the sheet more predictable.
- Fewer rejections. At 0.5% prohibitives there is less room for the wax or plastic that turns a shipment into a claim.
Whether that premium is worth paying depends entirely on what the mill is making. A liner machine running at speed with tight strength targets will pay for grade 12 and still come out ahead. A mill producing lower-specification board may be better served buying grade 11 and accepting the yield.
Where the two grades come from
Grade 11 is collected broadly. Grade 12's definition names supermarket, industrial and commercial sources, and that is not incidental — those streams produce corrugated in a more uniform condition, with less of the mixed packaging that residential collection brings with it. The sorting that follows is what completes the grade, but the starting material matters.
In practice this means grade 12 is less available than grade 11, and availability moves with the collection streams rather than with demand. A buyer who needs a steady monthly position in grade 12 should contract it as a position rather than buying spot.
How to avoid the argument at the discharge port
Most disputes over corrugated are not disputes about the material. They are disputes about what was agreed. Four habits remove nearly all of them:
- Contract the grade number. Not "OCC", not "clean corrugated" — #11 or #12.
- State both tolerance figures on the offer. If only one number appears, the other is being left to interpretation.
- Agree tighter limits in writing if the mill needs them. A verbal "it'll be clean" is not a specification.
- Confirm the destination's own requirements before booking. Contamination limits and import conditions vary by market and change over time; they sit on top of the ISRI grade, not inside it.
We trade both grades, and we state the grade number and both tolerance figures on every offer. The full grade table, including SOP, SWL and the three mixed paper grades, is on the waste paper page.