How Much Grease Resistance Does Your Carton Actually Need?

Buy a few grease-heavy products off a store shelf and look at the inside of the cartons. Some of what's shipping today shows less grease hold-out than we'd historically have called acceptable. We've bought the samples and checked.

It lines up with what we hear in quoting conversations: brands willing to accept a lighter grease barrier than their category used to carry, because the thing that provided the heavier one — a polyethylene layer on the board — now costs them somewhere else. Recyclability. Plastic-reduction commitments. Extended-producer-responsibility laws that price packaging by what it's made of. The grease spec is getting weighed against all of that, and for some products, the grease spec is losing.

Coating suppliers see the same thing from their side of the market — one told Food Engineering that some brands now choose lower-spec barrier options simply because they don't need the level of protection they'd been buying.

Grease resistance is a dial, not a switch

The industry measures grease hold-out with the kit test, TAPPI T 559. A lab places drops of twelve numbered solutions on the sheet, each blend more aggressive than the last, wipes each drop away after fifteen seconds, and looks for staining. The board's KIT rating is the highest-numbered solution that leaves no mark. The scale runs 1 to 12: higher, more hold-out.

What matters about the scale is that it exists at all. Grease resistance isn't a yes-or-no property. Products sit at different points on the dial depending on fat content, contact time, and temperature — a donut box, a frozen fried-chicken carton, and a scoop container don't need the same number. For decades, though, the practical board choices clustered near the top of the dial, so specs defaulted there — and a spec, once written, tends to get inherited by the next project rather than re-derived.

Why poly-coated board became the default

Poly-coated board is paperboard with polyethylene extruded onto it — a thin, continuous plastic film bonded to the sheet. As a grease and moisture barrier it is hard to beat: it holds out hot, heavy, prolonged grease contact that lighter coatings don't reach, it blocks moisture at the same time, and it has decades of proven performance behind it. If a carton in your category has carried a serious grease barrier for a long time, this is probably how.

The trade-off is that the polyethylene is still there when the carton's job is done. To recycle the fiber, the film has to be separated from it, and the mixed-paper streams most recycling programs run aren't set up for that — so poly-coated board is shut out of most of them. That's not an outside critique; it's the industry's own assessment. In 2023, producers and brands including Sonoco, Procter & Gamble, and General Mills formed the Poly-Coated Paper Alliance to push for wider end-market acceptance — an effort that exists precisely because acceptance today is limited and inconsistent.

None of that makes poly-coated board the wrong choice. For heavy grease it is often still the only choice. It just means the barrier is no longer free — and buyers have started doing the math.

A mid-range answer with no PE layer

This is the gap we've added a board for: a grease-resistant SBS that carries a barrier coating on the back side of the sheet — no polyethylene anywhere in the construction. The mill rates it KIT 7. On the 1-to-12 dial that's solidly mid-range, and the mill's own end-use list runs from bakery boxes to food-service trays and scoops. We're starting with bakery and general food-service work.

Because the barrier is a coating rather than a film, the sheet itself is still SBS paperboard, not a laminate: a clay-coated print surface on the front, in 12 to 20 pt calipers. The mill lists the finished board as fully recyclable in standard paper streams. What that means for the claim on your package is a separate question: recyclability labeling is the brand owner's determination under laws like California's SB 343, and we supply the board documentation that supports it. Our EPR article covers how those laws sort packaging.

Where poly-coated board still wins — for now

What you give up relative to poly-coated board is headroom. KIT 7 is not KIT 12, and it isn't trying to be. Heavier exposures — long hot holds, saturated-fat contact across a full shelf life, anything that sits wet against the board — sit higher on the scale, and for those applications poly-coated board may still be the right spec for now.

We quote both boards, and we'll tell you which one your product actually needs.

How to find your number

The useful question isn't “what's the most grease resistance we can get?” It's “what does this product actually do to a carton?” Fat content, contact time, temperature, and whether the product touches the board directly or through a liner or bag. If the honest answer is mid-range, the grease spec no longer forces a polyethylene layer into the package.

So if your current carton runs on poly-coated board, the question worth asking is whether the PE layer still earns its place. Sometimes it does. But if your product sits mid-dial, there's a substrate without the polyethylene now — you give up grease headroom you may not have been using, and the carton sheds the layer that complicates recycling, counts against plastic-reduction goals, and figures into state EPR fee schedules. That's worth exploring before the next reorder.