A greaseproof paper bag is chosen for one job: keeping oil from reaching the shelf, the counter and the hands carrying it. The catch is that “greaseproof” is a class, not a single grade—a bag that stops a light smear on a cookie may weep the moment fried food sits in it. The deciding factor is how much oil and how long the contact lasts. Grade the bag to the oiliest, longest contact your product makes, test it with the real fill, and you avoid the two failures: oil bleeding through, or paying for a heavier bag than the job needs.
What oil does to a paper bag
Oil moves through a paper bag in two ways, and they call for different answers:
- Seepage. Free oil wets the sheet and travels to the outer face, leaving a stain your customer sees on the shelf.
- Wicking. Oil creeps along fibres and folds—especially the bottom gusset and the seal—and can reach the bag's edges even when the face looks clean.
Both are graded by a grease-resistance test, and both get worse with heat. A bag that holds a cold pastry has no information about how it behaves with a hot one, which is why the temperature of the fill is part of the spec, not an afterthought.
How to judge the grease class
Typical checks (always confirm with a batch test on your real product):
- Oil level: light (dry pastries) needs less than heavy (fried items, deli meats with visible surface oil).
- Contact time: how long the product sits packed before it is opened changes the class you need.
- Heat: warm or hot fill lowers the barrier—see greaseproof-plus-heat below before committing a grade.
Ask the supplier for the test method behind any “greaseproof” claim, and run a spot-on-your-own-pack check for the two or three items that define your line. The label is a class; the test is the evidence.
Choosing by oil level
| Content | Oil contact | Grease class | Grammage | Best bag |
|---|---|---|---|---|
| Dry pastries, biscuits, crackers | Light, dry surface | Low | 60–80 gsm | Greaseproof kraft, light grade |
| Buttery cookies, croissants, baked confection | Light, oily touch | Medium | 80–100 gsm | Greaseproof kraft, standard |
| Deli meats, fried snacks, oily prepared foods | Heavy, visible oil | High | 90–110 gsm, often lined | Greaseproof or lined bag |
| Hot-fried food, warm bakery out of the oven | Heavy + heat | High, needs heat | Check heat handling | Greaseproof-plus-heat (see below) |
Read across from your oiliest item, not your average one—the average is the one that lets leaks sneak through on the heaviest day.
When heat joins in
Greaseproof paper resists oil at moderate and chilled temperatures; it is not built to carry a hot fill. If a product goes into the bag warm or hot, the oil is thinner and the barrier shrinks, and you are really asking a different question—grease plus heat together. That is the moment to reach for a parchment paper bag, which pairs oil resistance with heat handling rather than a plain greaseproof grade.
Common misuses and boundaries
- One greaseproof bag for everything. Greaseproof is a class; grade it to the oiliest, longest contact on the line.
- Judging by the face. A bag that looks clean can still be wicking oil along the bottom fold—inspect the folds and the seal, not just the front panel.
- Treating greaseproof as a heat answer. For a hot fill, add a parchment upgrade instead of asking a single greaseproof grade to do both.
FAQ
Is a “greaseproof” label enough to trust?
No single grade sits behind the word. Ask for the test method and confirm the class against your oiliest, longest-contact pack before you commit a run.
What grammage do I need for oily fried food?
A high grease class at 90–110 gsm, often with a lining, is a common starting band; the true grade comes from a batch test with your actual fried item.
Can a greaseproof bag hold hot food?
Greaseproof resists oil at moderate and chilled temperatures; a hot fill needs a paper that handles heat too—see parchment paper bags.
Does a lining always fix grease?
A lining raises the barrier and can help heavy oil, but it often adds cost and changes the recycling message—confirm both the oil test and the sustainability claim you intend to make before adopting it.
Browse the range
Start with greaseproof paper bags for the oil barrier, or parchment paper bags once heat joins the fill. For a natural carry see kraft paper bags; the whole line begins at eco paper bags.