Key takeaways
- A liner makes cosmetic condition irrelevant, which lets you buy a grade lower and saves four to five dollars against a two-dollar cost.
- It also protects the board from the product, which adds roughly two trips across our own placed stock.
- Gauge follows abrasion, not product value: 3 mil tears on regrind and leaves film fragments in the material.
- Liner sizing follows inside dimensions plus fill allowance plus gussets — send the box size, not a liner dimension.
A four-mil poly liner for a 48 × 40 × 36 box costs somewhere between $1.40 and $2.20 depending on volume. It does three things, and each one is worth more than it costs.
One: it makes cosmetic condition irrelevant
The main reason people buy 1A or 2A when 3A would do is that the interior has old labels, scuffing or previous product marks. A liner puts a physical barrier between your product and all of that.
Which means the grade decision collapses to structure alone — and structurally, a dry 3A box carries the same load as a 1A. The saving is typically four to five dollars a box against a liner cost of two.
Two: it protects the board from your product
This is the direction people forget. Abrasive material scours the inner liner. Fine powder migrates into the flutes and never comes out. Anything with moisture in it transfers that moisture into the board, which is the fastest route to a box that grades a rung lower next time.
A lined box comes back from a trip in noticeably better condition than an unlined one carrying the same material. Across our own stock the difference is roughly two additional trips.
Three: it solves the contact question
For a large share of food, ingredient and intermediate applications, a certified liner is how the industry handles contact requirements while using graded used containers for the structural job. It is not a workaround; it is the standard approach, and your quality team will have a written position on it.
| Gauge / type | Use | Handles | Typical cost |
|---|---|---|---|
| 2 mil poly | Dust control, dry gentle product | Light filling | $0.85 – $1.20 |
| 3 – 4 mil poly | General purpose, resin, regrind | Most operations | $1.40 – $2.20 |
| 5 – 6 mil poly | Abrasive, heavy, auger-filled | Rough filling and tipping | $2.40 – $3.60 |
| Foil / metallised | Hygroscopic powders, ingredients | Moisture and light barrier | $4.50 – $8.00 |
| Antistatic | Fine powders, electronics | Charge dissipation | $3.20 – $5.00 |
| Vented | Warm product equilibrating | Condensation control | $1.90 – $2.80 |
Getting the gauge right
Gauge follows abuse, not product value. The most common mistake is specifying three mil for regrind, which tears on discharge and then leaves polyethylene fragments in the material — a problem considerably more expensive than the liner.
The second most common is buying six mil for everything, which is a fifty per cent premium over what most applications need.
Gussets and sizing
Liners are sized to inside dimensions plus a fill allowance, with gussets so the corners are actually reachable. A liner that is nominally correct but has no gusset allowance bunches, which wastes corner volume and tears where it folds.
Send us the box size and what goes in it rather than a liner dimension. Specifying gussets is our job and it takes us thirty seconds.
Where liners do not help
- Direct contact with unpackaged food where the specification requires new board. A liner does not create traceability.
- Structural problems. A liner does nothing for a crushed edge or damp board.
- Very hot product, where the film can deform or bond to the material.
- Applications where the liner becomes a contamination issue in its own right — some recyclers will not accept lined boxes without separation.
Questions