A distributor in Rotterdam sent back our sample carton last spring. Hinges were cracking at the fold on roughly one box in thirty. The cause wasn’t the material — our pressing dies were running a hair too dry on that SKU, so the fibre at the hinge line had no room to flex. We re-set the moisture window and the hinge went quiet. That is the point of this guide: a clamshell is a set of moulding choices, not one product.
What a clamshell really is
One pressed piece: base, lid, and a living hinge, closed with tabs or a snap lock. Base and lid come off one mould, so the box opens flat and stacks nested when shut — no separate lid to match, better freight density. Two decisions drive most complaints. Wall thickness: thinner walls cool faster and press cheaper, but the hinge and lock tabs lose flex. And one-piece versus two-piece joined at a score — one-piece is what buyers mean by “clamshell.”
Compartment options
Single-compartment is the standard box: one open well, one lid — rice bowls, noodle kits, food that tolerates pooled liquid. The 3-compartment version adds two shallow side wells to a main well, what restaurants order for a protein and two sides; dividers are pressed from the same sheet, not glued in, because glued dividers fail under hot oil. A 2-compartment split exists, but volume per mould is thinner — most buyers settle on 3-comp.
Size matrix
Directional numbers; dimensions, gram weights, and temperature tolerance vary by SKU.
| Lid fit | Microwavable | Oven | |||
|---|---|---|---|---|---|
| 6″ | 1 or 3 | 8–11 g | tab lock | yes, short reheats | no |
| 8″ | 1 or 3 | 12–16 g | tab lock | yes | no |
| 9″ | 1 or 3 | 16–22 g | tab + partial snap | yes | no |
| 9″ heavy | 3 | 22–28 g | full snap | yes | brief, dry heat only |
Microwave tolerance sits around 100 °C food temperature on short cycles — 2–3 minutes, not a 20-minute reheat. Above roughly 120–130 °C the fibre softens and the hinge can sag. Oven use is dry, low, short, or not at all; only the heavy 9″ goes near warm-holding cabinets (subject to specific SKU).
Oil and leak resistance — the honest version
Bagasse is not a plastic tub, and pretending otherwise gets you returns. The fibre resists oil up to a point: fried food sits fine for a normal delivery window. Pooled thin liquid — broth, soup, curry — wicks through the base seam over time unless the box carries a coating or laminated liner. Some SKUs use a water-based barrier layer; others are uncoated. Straight talk: a soupy menu wants a lidded bowl, not a clamshell.
What to test when you sample
Ask for a sample in the actual gram weight you’ll buy, not a heavy “marketing” sample. Then:
- Fill with hot, oily food, close, wait 30 minutes. Check the hinge line and base seam.
- Stack five loaded boxes for an hour. Check lid lift and tab pop.
- Microwave loaded 2–3 minutes. Check hinge sag and base softening.
- Tilt 45° and shake — catches lock tabs that open under movement.
- Flex the hinge 20 times. It should not whiten or crack.
If a sample fails on hinge flex, that’s a moulding parameter problem, not a material verdict — ask the factory to adjust moisture and press dwell.
Certifications and compliance
For EU orders we typically hold EN 13432 and OK Compost HOME; BPI covers the US market. Food contact is FDA (21 CFR) for the States and LFGB for Germany. We provide declarations against the specific SKU — the reference lives on our compostable certification standards page, and the home-versus-industrial split is in our home vs industrial composting note.
MOQ, lead time, and OEM
Stock moulds start at a lower per-SKU minimum; a custom compartment layout or new print die raises it and adds tooling lead time. Production typically runs the low weeks after artwork sign-off, plus sea transit — FOB Qingdao is usual. We print OEM on lid and base. Freight from Qingdao has swung a lot since 2024.
FAQ
Are bagasse clamshell lunch boxes microwave safe?
Yes for short reheats, around 100 °C food temperature and 2–3 minutes.
Can a clamshell hold soup or curry?
Not reliably without a barrier coating. Pooled thin liquid wicks through the base seam.
What gram weight should I order?
Match it to the load. A light 6″ for pastries can be 8–11 g; a loaded 9″ bento wants 16–22 g.
Do you offer 2-compartment versions?
We can, but the mould volume per shape is thinner than 1- or 3-comp, so tooling lead time is longer.
What is your MOQ and lead time?
Flexible, and it depends on stock mould versus a custom print die. Production runs a few weeks after artwork approval, plus sea freight.
Are the boxes certified compostable?
We supply EN 13432, OK Compost HOME, and BPI documentation, plus FDA and LFGB food-contact declarations, matched to the specific SKU.
Sourcing a clamshell is a spec conversation, not a catalogue pick. Send your menu, gram weight, and stacking assumptions, and we’ll tell you which mould fits. Start with a sample request, or contact us if you’re comparing two sizes for the same chain.
