Decision one — gauge
Two mil for dry, light, non-abrasive goods. Three to four mil for powders, pellets and produce — the general-purpose range, and the usual starting point. Five to six mil for sharp edges, heavy loads, or any product that will be dragged during discharge.
Over-gauging is wasteful but harmless. Under-gauging fails at the bottom corner, usually on the second fill, usually in front of a customer.
Decision two — gusset
A gusseted liner opens to the full footprint and sits into the corners. Free-flowing product in a flat liner bridges across the corners, then settles unevenly and pushes the body out of square. If your product pours, specify a gusset.
Decision three — grade
If the liner will touch food, check current regulations and ask the supplier for resin documentation. Clear film is not a credential: appearance tells you nothing about the resin. Antistatic film is commonly used for resin pellets, both to prevent clumping and to avoid discharge hazard during transfer.
Decision four — length
Liner height should exceed box interior height by at least eight inches so the liner can be gathered and closed above the fill line. A liner cut flush to the box is one of the most common liner problems, along with under-gauging.
- 36" box → 44" liner minimum
- 40" box → 48" liner minimum
- 44" box → 52" liner minimum
- Add 4" more if the liner will be twist-tied rather than folded
