Why grease is its own problem
Water and grease behave differently against packaging. Water beads on many surfaces and is stopped by a simple coating. Oil wets surfaces, travels along fibres and seams, and gets hotter than water in the same dish. A box that holds soup without trouble may show dark stains through its walls after twenty minutes with fried food. For plastics the issue is less about penetration and more about heat and migration: oily food carries more heat to the container wall in reheating, and fatty food is the toughest case in a migration test.
So grease resistance is two questions. For paper and fibre: does oil pass through, stain the outside or soften the board? For plastics: does the container keep its shape with hot oily food, and does its food contact file cover fatty foods?
How the takeout materials compare
| Material | Reference items | Grease behaviour | What to confirm |
|---|---|---|---|
| PP | 750 ml box 170x115x51 mm; roast-meat box 217x149x60 mm | Oil does not pass through; heat is the limit | Shape with hot oily food; fatty simulant in migration test |
| PET | Clear clamshells, cold lids | Oil does not pass through; cold use only | Not for hot fried food |
| Kraft or white card, uncoated | Bakery box 190x85x35 mm | Oil can pass and stain | Dry items or a liner |
| White card with foil lining | Click-lock boxes 350-2,880 ml | Lining acts as a barrier on the inside | Seams and fold lines |
| Coated board | Click-lock and pizza boxes | Depends on the coating | Coating chemistry and PFAS statement |
| Starch-PP blend | 800 ml bowl 175x125x56 mm | Per supplier statement | Surface and shape after hot oily fill |
The roast-meat boxes in the reference range, 1,200 ml at 217x149x60 mm and 35 g and 1,500 ml at 217x149x71 mm and 39 g, are heavier than the 750 ml box for a reason: they carry hot, fatty food that loads the base and corners. That is the general pattern for PP. When the food is oily and hot, hold or raise the gram weight rather than cutting it. See PP food containers.
Paper boxes and barriers
Paper boxes from the printing and packaging cluster around Longgang near Wenzhou are made in kraft, white card and white card with a foil lining. Click-lock takeout boxes in the reference range run from 350 to 2,880 ml, some with two compartments, and pizza boxes from 6 to 12 inches, about 20x20x4.5 cm to 32x32x4.5 cm. For dry bakery items, uncoated board is usually enough. For fried and oily food, the box needs a barrier on the food side: a lining, a coating or a separate liner sheet.
The weak points are the folds and seams. A flat panel with a good coating can still let oil through at a crease where the coating cracked during folding, or at a glued seam. That is why grease checks are run on folded, assembled boxes filled with the real food, not on flat board samples. The folding and bakery boxes page lists the board grades.
PFAS and grease resistance
For many years, a common way to make paper and fibre packaging resist grease was to treat it with fluorinated chemistry, part of the PFAS family. That route is closing in the United States. California AB 1200 has banned intentionally added PFAS in plant fibre food packaging since 1 January 2023, with a screening line of 100 ppm total organic fluorine. At least 13 states restrict PFAS in food packaging in some form, including New York, California, Washington, Colorado, Connecticut, Maryland, Minnesota, Hawaii, Oregon, Rhode Island, Vermont, Maine and New Hampshire, and Vermont, Connecticut and Minnesota extend their rules to all food packaging materials. State wording varies and changes, so confirm the current rule for each destination with counsel.
In practice, every paper or molded fibre item for the US needs a written statement from the partner plant that no PFAS has been intentionally added, and where a buyer wants evidence, a total organic fluorine test. Barriers then come from other routes: linings, alternative coatings or a liner. The PFAS note covers the state rules in more detail.
Testing for grease
A practical grease check is agreed per order and run on the assembled item:
- Fill the box with the real food or an agreed oily test food at serving temperature.
- Close it as it would be closed in service and hold for the agreed time, for example the longest delivery time.
- Check the outside for staining, especially at folds, seams and the base.
- For plastics, check shape and lid fit with the hot oily fill.
- For paper, check stiffness after the hold, since softened board crushes in a delivery bag.
For the food contact file, the migration test for a container that will hold oily food should include the fatty food simulant; see migration testing explained.
Print, labels and the outside of the box
Grease also reaches the outside of the pack in less obvious ways. Hands that have touched fried food leave marks on printed lids and sleeves, and oil from one container can stain the label of the next in a crowded delivery bag. Printed paper sleeves on PP boxes, and printed kraft boxes, should be checked for print rub and staining with oily fingers, not only with water. Sauce cups and small lidded portions are often the real source of leaks in a bag; their lid fit deserves the same tilt check as the main box, and results are described as leak-resistant in that test, confirmed per order. On paper boxes, a darker kraft or a printed pattern hides light staining better than plain white card, which is a design choice worth making early for oily menus.
Choosing for the menu
For hot fried food, sauced dishes and curries, PP is the reliable choice because oil cannot pass through it; the questions are heat and gram weight. For fried food that needs to stay crisp, paper boxes with vents and a barrier are often preferred because a closed PP box traps steam. For pizza and bakery, coated or lined board fits, with the PFAS statement in the file. The plastic vs paper note compares the routes, and restaurant takeout sets out a full program.
Printed paper boxes typically start at 5,000-10,000 per design and stock PP boxes from a few cartons, confirmed in writing per program; send the menu through the quote form.