In short: Most custom plastic packaging bags are made between 0.03 mm and 0.10 mm (about 1.2 to 4 mil) single-wall thickness. Apparel zipper bags usually sit at 0.04–0.06 mm, die-cut handle shopping bags at 0.06–0.10 mm, and poly mailers at 0.06–0.08 mm. Always confirm whether a quoted figure is single-wall or double-wall, and in which unit, before approving a specification.
Thickness is the specification buyers most often get wrong, because several unit systems are in use at once: millimetres and microns in Asia and Europe, mil in North America, gauge in parts of the US and UK trade, and the Chinese factory habit of quoting in “si” (丝). The same 0.08 mm bag can appear on four quotes as 80 micron, 3.1 mil, 315 gauge and 8 si. This guide covers the conversions, the thickness each bag type usually needs, and how to write the figure into a purchase order.
Micron, Mil, Gauge and “Si”: Conversion Table
All four units measure the thickness of one film wall, and the relationships are fixed: 1 mm = 1,000 µm; 1 mil = 25.4 µm; 100 gauge = 1 mil; 1 si = 0.01 mm.
| mm | Microns | Mil | Gauge | Si (丝) | Typical use |
|---|---|---|---|---|---|
| 0.03 | 30 | 1.2 | 120 | 3 | Thin zipper bags, OPP self-seal bags |
| 0.05 | 50 | 2.0 | 200 | 5 | Standard apparel zipper bags |
| 0.06 | 60 | 2.4 | 240 | 6 | Poly mailers, retail zipper bags |
| 0.08 | 80 | 3.1 | 315 | 8 | Die-cut handle bags, premium mailers |
| 0.10 | 100 | 4.0 | 400 | 10 | Heavy-duty handle bags, hardware packaging |
Heyi Custom Bags runs film from 0.01 mm to 0.2 mm at its factories in Dongguan, China and Haiphong, Vietnam, so every value on this table is within range.
Single-Wall vs. Double-Wall: The Most Common Quotation Trap
A bag has two walls. Some suppliers quote one wall; others quote both together, which doubles the number. A quote that says “0.12 mm” can mean a 0.06 mm single-wall bag or a much heavier 0.12 mm single-wall bag, and the difference in material cost and strength is roughly double. In the Chinese trade, double-wall figures are common for die-cut handle bags and are often not labelled. The safe practice is to state the figure explicitly, for example “0.06 mm single-wall (12 si double-wall)”, and to convert every competing quote to single-wall microns before comparing. Heyi Custom Bags quotes single-wall thickness by default and labels it on every proforma invoice.
Recommended Thickness by Bag Type
- Zipper bags for apparel and accessories (LDPE, CPE, PP): 0.04–0.06 mm. A T-shirt bag at 0.05 mm feels substantial without bulk; frosted CPE at the same thickness feels softer in the hand than LDPE. See our clear PE zip lock bags.
- Die-cut handle shopping bags: 0.06–0.10 mm for LDPE; 0.03–0.05 mm for HDPE. A 0.08 mm LDPE handle bag comfortably carries 3–5 kg of boxed goods. Standard sizes are on our die-cut handle shopping bags page.
- Poly mailers (co-extruded PE): 0.06–0.08 mm. Below 0.05 mm the corners tear in sorting machines; above 0.10 mm the extra weight rarely adds protection. See custom poly mailer bags.
- Self-adhesive OPP bags: 0.03–0.04 mm; OPP is stiff and clear, so it does not need to be thick.
Material, Cost and Printing
The same thickness performs differently by resin: HDPE is stiffer per micron, so a 0.04 mm HDPE carrier can match a 0.08 mm LDPE bag in load capacity, while LDPE prints more smoothly. Compostable PLA/PBAT film is less stretchy than PE and is usually run at 0.03–0.06 mm, so do not copy a PE specification across unchanged. Resin is the largest cost component of a bag and scales almost linearly with thickness: moving from 0.06 mm to 0.08 mm uses about one-third more material and adds freight weight on shipments to the USA, UK, Canada, Australia and the EU. Film below 0.03 mm also stretches during gravure printing, so for 6–10 colour designs we recommend at least 0.04 mm.
How to Specify Thickness on a Purchase Order
- Write the value in millimetres with the single-wall qualifier, for example “0.06 mm single-wall”, adding mil in brackets for North American colleagues.
- State the tolerance you accept; ±10% is usual for film, and the factory should confirm its figure in writing.
- Approve a physical sample at the exact thickness before signing off the production file.
- Ask for micrometer readings at three points on the bag in the pre-shipment inspection report.
Heyi Custom Bags has a fixed MOQ of 5,000 pcs per design and serves brand owners, wholesalers and distributors buying at volume, with a lead time of 15–25 days after artwork approval. For more detail on carrier bags, read our LDPE vs. HDPE die-cut handle bag guide.
FAQ
What is the difference between mil and micron for plastic bags?
One mil is one thousandth of an inch, or 25.4 microns; one micron is one thousandth of a millimetre. A 2 mil bag is therefore about 50 microns or 0.05 mm thick.
Is bag thickness measured on one wall or both walls?
Thickness should be measured and quoted on a single wall of film. Some suppliers quote double-wall figures, which doubles the number, so always ask which convention a quote uses before comparing offers.
What thickness should a custom printed zipper bag for clothing be?
Most apparel zipper bags are made at 0.04–0.06 mm (1.6–2.4 mil) single-wall. This gives a solid feel and protects the garment without adding unnecessary material weight.
What is “si” (丝) in a Chinese plastic bag quotation?
Si is a traditional Chinese thickness unit equal to 0.01 mm or 10 microns. A quote stating “6 si” means 0.06 mm, but check whether it refers to one wall or two.
Get the Right Thickness From Heyi Custom Bags
Heyi Custom Bags has made custom zipper bags, die-cut handle bags, poly mailers and pouches since 2016, with three production bases in Dongguan, China, one in Haiphong, Vietnam, around 500 staff, and ISO 9001, ISO 14001 and GRS certification. Send us your bag size, material, print colours and quantity, and we will recommend a thickness, confirm it as single-wall in writing, and ship physical samples before production. Request a custom zipper bag quote, or use our general quote form for other bag types.