Packrift · Poly Bag Guide

Soft, light goods that ride inside another shipper — apparel, textiles, paper, counted parts that mainly need a clean layer — 2 mil is enough. Step up to 4 mil when the contents have corners, threads, or weight, or when the same bag gets opened, binned, and handled again and again. The difference is material: a 4 mil wall is 0.004" of polyethylene per side, twice the 2 mil wall, and that margin is what survives hardware edges and warehouse cycles.

SCOPE — this page compares poly bag wall thickness. Searching 6 mil vs 4 mil for film that covers floors, dust walls, or pallets? That is sheeting — use 6 mil vs 4 mil plastic sheeting. Heavier bags are compared on 4 vs 6 mil poly bags.

Which thickness for the job → Formats & closures How to pick Sheeting instead? 6 vs 4 mil film Shop poly bags
FIG. 1 — BAG WALL CROSS-SECTION · RELATIVE SCALE A A · 2 MIL BAG clean inner layer · soft goods B B · 4 MIL BAG corners · weight · reuse same bag at arm’s length — the wall is the difference DETAIL A 2 MIL 0.002 in per wall DETAIL B 4 MIL 0.004 in per wall 2× the material wall cross-sections drawn to relative thickness — 2 : 4 a poly bag is two walls of film
01 — START WITH THE CONTENTS

Which thickness for the job

Start from what goes in the bag and how often it gets handled, not the number on the case. Find your row, read the verdicts, start with a real SKU.

What the bag holds 2 mil 4 mil Start here
Apparel & soft goodsfolded tees, textiles, plush — riding inside a mailer or box BestCleanliness and presentation; the outer shipper takes the abuse. SkipMaterial the shipment never uses. 14×18" 2 mil flap-lock → 18×24" 2 mil flap-lock →
Small parts, kits & resalecounted picks, cards, samples, order slips BestWrite-on block for part numbers; zip survives a few openings. OKStep up when the same bag is opened over and over. 4×6" 2 mil reclosable → 6×9" 2 mil reclosable →
Hardware & sharp cornersbolts, fittings, machined parts, threaded stock RiskyThreads and corners find a 0.002" wall — one puncture spills the count. BestTwice the wall where point pressure actually lands. 4×6" 4 mil reclosable → 8×10" 4 mil reclosable →
Bin cycles, returns & pegsrepeated warehouse picks, inspection, retail peg display OKFine until open-close cycles and bin rub add up. BestStiffer wall, tougher zip — and the hang-hole versions live here. 9×12" 4 mil + hang holes → 4×6" 4 mil + hang holes →
Big liners & long storage24×36 carton liners, equipment parts, off-season stock SkipBig spans multiply corner load and drag. BestHolds a load-out at liner scale; storage creases don’t split. 24×36" 4 mil flat → need more? 24×36" 6 mil →
Electronics (ESD)boards, components — pink anti-static line BestBoards and small components inside other protection. OKStep up for heavier assemblies and connector edges. 8×10" 2 mil anti-static → 8×12" 4 mil anti-static →

If a lighter bag already failed on a SKU — split seam, corner puncture, zip fatigue — that is the answer; buy the next mil up and stop testing. Comparing film for floors and dust walls instead? That is the 6 mil vs 4 mil sheeting page. Bags heavier than 4 mil are on 4 vs 6 mil poly bags.

02 — UNITS, FORMATS & CLOSURES

Thickness, format, and closure

Mil is the unit; the closure decides how the bag works on the bench. Every SKU below is real and in the Packrift catalog — open one for current dimensions and case counts.

The unit

Mil, gauge — and two walls

A mil is one thousandth of an inch, measured per wall. A 4 mil bag is 0.004" of polyethylene on each side — but corners and threads press on one wall at a time, so the per-wall number is the spec that matters.

  • +4 mil = 0.004" per wall — exactly twice the 2 mil wall.
  • +Stretch film uses gauge for the same idea: 100 gauge = 1 mil.
  • −A mil is not a millimeter — 2 mil is about 0.05 mm.
  • −The same unit rates sheeting, tubing, and tape backing — check what the number is attached to.

Terms before specs: packaging glossary

Slide in · tape, seal, or fold

Flat open-end bags

The plain workhorse: an open mouth, no closure hardware, priced for volume. At 2 mil the line adds colors — black, white, red, blue, yellow, green — so teams can color-code parts bins without labels.

  • +Fastest bag on a packing bench — slide in, fold or tape.
  • +Colored 2 mil doubles as visual sorting; black also hides contents.
  • +4 mil clear steps up to 24×36" liner duty.
  • −No reseal — one open is the open.
  • −A 1 mil food-grade tier exists below this page for produce-weight jobs.
Real SKUs 9×12" 2 mil black flat · 1000/case→ 6×9" 2 mil white flat · 1000/case→ 24×36" 4 mil clear flat · 200/case→

Browse: poly bags collection · black poly bag options

The 2 vs 4 decision lives here

Reclosable zip-top bags

The deepest run in the catalog — white-block write-on bags from 2×2" to 24×24", with most sizes stocked in both 2 mil and 4 mil. Same size, same closure, one variable: the wall.

  • +White block takes pen or marker — part numbers travel with the bag.
  • +Same-size pairs (6×9, 9×12…) make a clean thickness A/B.
  • +4 mil versions add hang holes for peg display and shadow boards.
  • −Zips fatigue before walls do — heavy reuse wants the 4 mil zip.
Real SKUs — same size, both walls 9×12" 2 mil reclosable · 1000/case→ 6×9" 4 mil reclosable · 1000/case→ 12×18" 4 mil reclosable · 500/case→

Heavier contents: 4 vs 6 mil poly bags

Static-safe variant

Anti-static (pink ESD) bags

The same 2 vs 4 mil ladder, tinted pink and formulated to bleed static instead of building it. Flat bags from 2×3" to 30×36", plus anti-static tubing when boards run long.

  • +2 mil for boards and small components inside other protection.
  • +4 mil where connector shells and standoffs press the wall.
  • −Anti-static is not shielding — the pink tint dissipates, it does not block fields.
Real SKUs 8×10" 2 mil anti-static · 1000/case→ 8×12" 4 mil anti-static · 1000/case→

Browse: e-commerce & fulfillment

Item has depth — or an odd length?

Forcing a boxy or extra-long item into a flat bag turns thickness into the wrong fix. Gusseted bags expand at the sides for depth (Packrift’s clear gusseted line runs lighter, at 1 mil), and 4 mil poly tubing cuts and seals into a bag of any length — dowels, trim, extrusions. Fit first; then pick the wall.

Poly tubing →
03 — HOW TO PICK

How to pick poly bag thickness

Five checks, same order every time. Most wrong buys start at step one with the wrong suspect — the wall usually isn’t it.

1

Start from the edges, not the number

Soft and folded means 2 mil. Corners, threads, machined edges, or anything that rattles means 4 mil. The bag fails where a point loads one wall.

2

Count the touches

Packed once and shipped inside a box — 2 mil rides protected. Binned, picked, inspected, returned, or hung on a peg — cycles are load; step up to 4 mil before the zip or wall quits.

3

Size before you thicken

A tight 2 mil bag fails on corners a right-sized 2 mil bag survives. Add about an inch of width and two of length for closure and hand room — the poly bag size chart and size & mil reference do the arithmetic.

4

Pick the closure for the workflow

Open-end for tape or heat-seal speed, flap-lock for apparel presentation, zip-top for anything reopened, hang holes for pegs. The closure changes daily work more than two extra mils do.

5

Run a case-level A/B

The reclosable line stocks the same sizes in both walls — order 6×9" or 9×12" in 2 mil and 4 mil, run both through real picks, and let the failed bag lose. Cheapest packaging experiment there is.

SIZE FIRST — THEN THICKNESS TIGHT — CORNERS LOAD THE WALL the fix is a size up, not a mil up +1" W +2" L SIZED — ALLOWANCE TAKES THE LOAD closure room, hand room, no corner strain

4 mil is twice the resin — and the case ships by weight and cube

Bags feel weightless one at a time; cases are not. At the same size and count, a 4 mil case carries 2× the polyethylene of its 2 mil twin — roughly twice the case weight on the same footprint. That is the honest cost of the margin: buy it for the SKUs with corners and cycles, not for the whole wall of bags.

Watch the case counts, too: the catalog drops from 1000 to 500 to 200 per case as bags get thicker and bigger, so a "case" is not a fixed quantity across mils. Carriers bill the greater of actual and dimensional weight; dense bag cases usually bill the scale, so thickness lands straight on the freight line. Bags ride along with boxes and tape on the same order — combine them so one charge spreads across everything. Sizing the outer carton is the other half: the box-size guide covers the outbound cube.

Open the cost & cube index →
THE THICKNESS-TO-WEIGHT TRADE
same size × same count:
4 mil ÷ 2 mil = 2.0× the film
≈ 2× the case weight
and carriers bill the greater of
actual lb vs (L × W × H) ÷ 139
(US domestic dim divisor)

Four mil around loose bolts is cheap insurance. Four mil around folded tees is freight with no job. Match the wall to the contents.

04 — QUICK ANSWERS

Poly bag thickness questions, answered

Should I use 2 mil or 4 mil poly bags?

Use 2 mil for soft, light, low-puncture contents that mainly need a clean layer — apparel, textiles, paper goods, counted parts riding inside another shipper. Use 4 mil when contents have corners, threads, or weight, when the bag is opened and handled repeatedly, or when a lighter bag has already failed on the same SKU.

What does 2 mil or 4 mil mean on a poly bag?

A mil is one thousandth of an inch of film thickness, measured per wall. A 2 mil bag has 0.002 inch walls and a 4 mil bag has 0.004 inch walls — twice the material. A mil is not a millimeter; 2 mil is about 0.05 mm. The same unit rates sheeting, tubing, and tape backing, so check what the number is attached to.

Are 2 mil poly bags strong enough for shipping?

Usually yes, when the bag is an inner layer: the mailer or carton takes the transit abuse, and the 2 mil bag only needs to keep contents clean and together. Ship a bag as the outer surface, or pack corners and hardware, and the margin disappears — that is 4 mil work, and sizing matters as much as thickness.

I searched 6 mil vs 4 mil — is this the right page?

Only if you mean bags. Most 6 mil vs 4 mil searches are about plastic sheeting — film rolls for floors, dust walls, crawl spaces, and pallet covers — which is compared on the 6 mil vs 4 mil plastic sheeting page. Heavier bags, 4 mil against 6 mil, are compared on 4 vs 6 mil poly bags.

Why do case counts drop as bags get thicker or bigger?

Cases are packed to a liftable weight and a sane cube, so counts fall as film per bag rises: 2 mil reclosable bags commonly come 1000 per case, larger 4 mil sizes drop to 500, and 24×36 inch 4 mil flat bags come 200 per case. Compare cost per bag and per-bag freight across mils, never case against case.

PACKRIFT · Match the wall to the contents, size before you thicken. Confirm current dimensions and case counts on each product page before ordering.