Liner spec by product: a starter list
A quick reference for matching the inner liner to what's going in the box. Two-mil poly is not for everything, and "food grade" is not a category.
If you're new to gaylord buying, the liner question is often the part that gets handled last and matters first. The wrong liner doesn't fail today — it fails three weeks into a contract when the product reaches its destination contaminated or compromised. This is a starter reference.
Standard low-density polyethylene (LDPE)
The default for most dry industrial product — resin pellets, fastener hardware, granular material that doesn't react to plastic. Sold in 2-, 4-, and 6-mil thicknesses. Two-mil for light product, four-mil for typical bulk, six-mil for sharp or heavy product that might tear a thinner liner.
FDA-grade LDPE
Required for any direct-contact food product. "FDA grade" specifically means the polymer chain has been verified as compliant with 21 CFR 177 regulations and there's documentation showing additives are food-safe. Standard LDPE is not FDA grade just because it's plastic. Ask for the documentation if you're shipping food.
Foil composite (kraft + aluminum)
Used when you need a moisture, oxygen, or grease barrier. Coffee, certain spices, pharmaceutical intermediates. Significantly more expensive than poly but performs differently. Don't confuse a foil-backed bag (impressive-looking) with a true foil composite (actually barrier-rated).
Anti-static / pink poly
Pink poly is anti-static LDPE, used for electronics, semiconductors, and aerospace components. The pink color is the color of the anti-static additive. Genuine anti-static liners include the additive throughout the thickness; cheap imitations have it only on the surface and fail after a few flexes.
Conductive (black poly)
A step beyond anti-static. Used for very sensitive electronics that need a path-to-ground. Specify the resistivity range — the spec language is "surface resistivity in ohms per square," and your engineering team will know the right range.
Open-top vs gusseted vs flat
Open-top is a tube sealed at the bottom. Gusseted has accordion folds on the sides that allow it to open wider when filled. Flat is exactly what it sounds like. Open-top is the most common; gusseted is what most large boxes actually want; flat is for slip-in applications.
Sealing
Heat-seal, twist-tie, zip-lock, or just folded over and taped — every method has a use case. Heat-seal is the most secure but requires equipment. Twist-tie is fast and adequate for most dry product. Zip-lock is consumer-style and not really suited to gaylord volumes. Tape-over-fold is the warehouse default and works.
Buying tips
Most buyers underspec the liner because the liner is invisible until it fails. If you're moving a product that's even slightly sensitive — to moisture, to electrostatic discharge, to chemical reaction with poly — pay the small premium for the right liner. The cost difference is almost always lower than the cost of one failed shipment.
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