An inquiry for "mixed paper" is one of the most common things to arrive on a trading desk, and one of the least useful. ISRI PS-2013 defines three separate grades under that heading. They are not interchangeable, their tolerances differ by a factor of four at the tight end, and they come from different places.
The three grades
| Grade | ISRI No. | Definition | Prohibitives | Outthrows + prohibitives |
|---|---|---|---|---|
| Residential Mixed Paper | #1 | A mixture of various qualities of paper, not limited as to type of fibre content, normally generated from residential multi-material collection programmes. | 2% | 5% |
| Soft Mixed Paper | #2 | A clean, sorted mixture of various qualities of paper, not limited as to type of fibre content. | 1% | 5% |
| Hard Mixed Paper | #3 | A clean, sorted mixture of various qualities of paper containing less than 10% groundwood content. | 0.5% | 3% |
Definitions summarised from ISRI PS-2013; tolerances as published.
Reading the definitions against each other
Two words do most of the work.
"Clean, sorted" appears in grades 2 and 3 and not in grade 1. Grade 1 is defined by where it comes from — residential, multi-material collection — and that origin is the specification. Nobody has gone through it afterwards. Grades 2 and 3 have been sorted, and the tolerance figures reflect it.
"Less than 10% groundwood" is the only quantitative composition limit in the three, and it is what makes grade 3 a different product rather than a cleaner version of grade 2.
What the groundwood threshold is actually about
Groundwood — mechanical pulp — behaves differently from chemical pulp in a recycled furnish. It carries lignin, which is what causes mechanical-pulp papers to yellow with light and age. Newsprint and much of the magazine stream are groundwood-containing; ledger, bond and most office papers are not.
A mill producing a product where brightness has to hold over time, or where strength matters more than bulk, wants the groundwood share controlled. The 10% ceiling in grade 3 is what gives it a contractual handle on that. Grade 2, which is "not limited as to type of fibre content", gives it none — a compliant grade 2 bale could be substantially groundwood.
Hard and Soft are not grades of cleanliness.
The names sound like quality tiers and they are not. "Hard" refers to the fibre composition — predominantly chemical pulp, low groundwood. A buyer who orders Soft Mixed expecting a lower-priced Hard Mixed has ordered a different furnish.
Why the distinction matters commercially
Mixed paper grades carry the widest definitional latitude of any part of the ISRI paper stock list. That latitude is precisely why the grade number has to be contracted. Two suppliers can both deliver lots that are honestly described as "mixed paper" and be delivering materially different products, both within specification for the grade each has in mind.
It is also why mixed paper generates a disproportionate share of inspection disputes. The argument is rarely about whether the lot met the grade. It is about which grade was agreed.
Specifying it properly
- Name the number: #1, #2 or #3. "Mixed paper" alone is not a contract term.
- If groundwood content is the constraint, contract #3 and state the limit. Do not rely on #2 arriving low in groundwood.
- State both tolerance figures on the offer, and agree any tightening in writing before booking.
- Agree the inspection point. Mixed grades are where the sampling location and method matter most, because the material is heterogeneous by definition.
We quote all three. The full grade table, including OCC, DSOCC, SOP and SWL, is on the waste paper page. The outthrows and prohibitives system that sits behind every one of these figures is explained in OCC vs DSOCC.