What to Look for in Co-extruded Shipping Bags

Poly mailers have become the default packaging for apparel, textiles, accessories, and other non-fragile goods sold online. They are light, waterproof, and space-efficient, which reduces both storage and freight costs. Yet the quality gap between products is wide. Two mailers with the same stated thickness can behave very differently in a sorting centre. Understanding how the film is made and which parameters matter helps a purchasing manager avoid costly returns and damaged parcels.

What co-extrusion means

Co-extrusion is a process in which several layers of polyethylene are formed together in a single pass rather than laminated afterwards. A typical three-layer film has an outer layer that resists scuffing and takes print well, a core that provides strength, and an inner layer that can be pigmented for opacity. Because the layers are fused, they cannot separate, and the film behaves as one material. The result is better tear resistance than a single-layer film of the same gauge, and often a lower material use for the same performance.

Thickness, strength, and opacity

Thickness is stated in micrometres, and most courier mailers fall between 40 and 80 micrometres. Light garments and soft goods are usually well served by around 50 to 60 micrometres. Heavier or bulkier products, or those with zips, buckles, or hard packaging, call for a thicker film. Beyond gauge, ask about puncture and tear resistance, because they depend on the polymer grade and process control. Opacity is another practical point. A grey or white inner layer hides the contents from view, which reduces the risk of theft and protects customer privacy.

Seams, closures, and tamper evidence

Weak seams are the most common failure point. Check that side and bottom seams are continuous and even, without thin spots. The closure should be a permanent adhesive strip covered by a release liner, ideally with a tamper-evident feature so that any attempt to open the parcel is visible. For returns-friendly shops, a second adhesive strip lets the customer reuse the same mailer. Test the adhesive at low temperatures if your parcels ship in winter, because some adhesives lose tack in the cold.

Sizes and packing efficiency

Choose sizes based on the products you ship most often, and leave a margin of 3 to 5 cm for the flap and for easy insertion. An oversized mailer increases the parcel volume and can raise carrier costs. Suppliers typically publish a size chart with tolerances, and it pays to compare it with your actual product dimensions. The technical specification and the available formats of Filmar’s range are listed at https://www.filmar-group.pl/en/products/courier-packaging/poly-maile-co-ex-filbags/, so you can check the details before requesting samples.

Printing and branding

Many online retailers order custom printed poly mailers. Printing turns the outer surface into a branding asset and can help discourage substitution during transit. When briefing a supplier, define the number of colours, the print area, the minimum run, and the type of ink. Water-based inks are a good option for polyethylene and support environmental goals. Approve a printed sample before releasing a full production run.

Recycled content and end of life

Sustainability targets and new EU packaging rules are pushing buyers towards mailers with recycled content. Post-consumer recycled polyethylene can match standard film on strength, although colour may vary slightly. Ask the manufacturer for the recycled percentage, documentation, and guidance on how the mailer should be disposed of after use, so that you can communicate this clearly to your own customers.

A practical buying checklist

Before placing a large order, request samples and run them through your real process. Pack typical orders, ship them with several carriers, and inspect seams, adhesive, and film condition on arrival. A producer that manages extrusion, conversion, and printing in-house can keep quality consistent from batch to batch and adapt specifications when your range changes.