Reclosable Poly Bags: A Mil Thickness Guide

"What mil thickness poly bag do I need?" is one of the most common questions we get on reclosable bags, and it's usually asked after someone already bought the wrong one — bags too thin for a part with a sharp edge, or bags too heavy (and too expensive) for something that just needed to stay dust-free. Mil thickness is the spec that actually answers the question; size alone doesn't tell you whether a bag will hold up.

BOXT stocks reclosable poly bags in nineteen size-and-thickness combinations at our Spanish Fork, Utah warehouse, sold by the case at wholesale pricing. Shipping outside Utah is standard — most orders arrive in 3–5 business days nationwide.

What "Mil" Actually Means

A mil is one-thousandth of an inch — it's the thickness of the plastic film itself, not the bag's size. Higher mil means more puncture and tear resistance, but also more cost and less flexibility. The right mil is about what's going inside the bag, not what looks "heavier duty" on the label.

Light Duty: 1.6–2 MIL

The economy tier — fine for small, non-abrasive items where the bag's job is organization or light dust protection, not structural durability. Small hardware, jewelry components, retail small parts. BOXT stocks this range from 1x1" up through 9x12".

Standard: 3–4 MIL

The middle ground and the most commonly ordered range — holds up to normal handling, stacking, and short-term storage without tearing at the seams. This is the default for general fulfillment packaging, retail small goods, and parts that will be handled more than once before they ship.

Heavy Duty: 6–8 MIL

For anything with a sharp edge, anything heavier, or bags that need to survive multiple open-close cycles without the zipper track failing. Hardware with machined edges, tooling, and components going into longer-term storage all belong here. It costs more per bag, but replacing a 2 MIL bag that split in transit costs more than the upgrade would have.

Matching Size to the Job

BOXT's catalog runs from 1" x 1" up to 9" x 12", with most sizes available across multiple mil thicknesses. A few sizing notes worth knowing before you order:

• Small parts (1x1" – 3x4") — hardware, fasteners, jewelry, small components. Usually paired with 2–4 MIL unless the contents are sharp.
• Mid-size (3x5" – 6x9") — the range most fulfillment operations reach for, covering small retail goods and multi-part kits.
• Larger (6x8" – 9x12") — bulkier components, multi-piece kits, or bags doubling as a mailer for lightweight product.

Getting the Combination Right

Undersizing the mil for the contents is the expensive mistake — a split bag mid-shipment means a damage claim or a return. Oversizing it just burns margin on material you didn't need. If you're not sure where a specific item lands, the safest move is to check what's actually going in the bag — weight, edges, how many times it'll be opened and reclosed — against the tiers above rather than defaulting to whatever mil you've always ordered. For bags built to ship product directly rather than just organize it in-house, our poly mailers guide covers that adjacent category.