At their simplest, box liners are gusseted polythene bags made to fit snugly inside standard boxes, trays, and reusable transport crates. They provide a protective barrier that outer packaging just can’t offer on its own.
But, as with so many things in the world of packaging – things aren’t always that simple! Box liners come in a few different flavours, and each one suits a specific job. Understanding these differences can help you pick the perfect one for your needs.
So, let’s get up close and personal with polythene box liners, and help you figure out thickness, sizing, and additives.
The purpose of box liners
An outer box provides mechanical protection – it takes the knocks, supports the stack, and gets the goods from A to B in a uniform manner. But boxes are made of cardboard (or some other material in a bid to be more eco-friendly), and these are not exactly world-renowned for being waterproof or contaminant-proof.
So, box liners are used to provide a moisture barrier. This barrier works in two directions – it keeps your goods safe from damp and contamination (even from the box itself), and it keeps the box dry if your product contains any moisture or grease.
Boxes with polythene liners are a very common partnership for a reason. The outer packaging provides the structure, while the inner liner provides environmental protection.
Box liners are brilliant at keeping contaminants out – dust, dirt, pests, you name it. A sealed polythene liner creates a clean, safe environment for your products. Plus, they make transferring goods from reusable transit crates an absolute doddle, because instead of having to tip everything out, you can just lift the liner out like a giant bag.
And that neatly brings us to the different types of box liners. We categorise our liners into three main types – but with polythene, almost anything is possible!
Types of box liners
Standard box liners
Designed to fit inside standard format cardboard boxes, standard box liners prevent leakages and keep the box clean and reusable or recyclable. By containing any spillages, they stop a single leaking product from destroying an entire shipment. They also keep external contaminants away from the product, which is vital in industries like food production and pharma. The polythene can be produced in a range of colours and tints, and can even be printed with your branding, instructions, or smart packaging QR codes for automation and tracking.
Dolav liners
We’re going to cover these separately in another post soon, because they’re probably the most different and misunderstood item on this list. But, for a quick overview, Dolav crates are basically those incredibly tough, light, and infinitely reusable plastic shipping crates you see everywhere – from supermarkets to the backs of Amazon vans.
They are fantastic bits of kit, but cleaning them out after a leak or spill can be a real pain. Dolav liners act as a protective barrier between the crate and the contents, allowing for a super quick transfer of products, and slashing cleanup times. The crate can get straight back to work, and the goods can be moved on to their next stage without any fuss!
Polythene tray liners
Polythene tray liners are similar to box liners, but they’re shallow and broad. They are designed specifically to fit in a tray, like the ones often found in the food and medical industries, where preventing leakages and contamination is absolutely critical. In fast-paced, lean operations, these liners allow workers to simply lift out the liner and its contents, and the tray is ready to be reused immediately. No washing, no waiting!
Custom integrations
One of the best things about box liners is how easily they can be customised to fit your exact needs. That’s because, for most businesses, a one-size-fits-all approach just simply does not cut it. But a custom box liner gives you a perfect fit, minimises waste, and maximises protection.
You can specify not just sizing, but thickness, too. So for heavier or sharper items, a thicker gauge of polythene can be used to offer total protection. Custom colours and printing can aid not just with looks, but with sorting and processing. And custom additives to the polythene masterbatch can enhance performance – anything from UV resistance, to low temperature tolerance, to antistatic additives that repel dust and protect electronics.
Box liners are a versatile upgrade that can take your operations to the next level. So – how do you measure and fit them?
Size calculator for box liners
Finding the right size of box liners off the shelf isn’t easy – especially because boxes are measured in three dimensions, and bags are generally measured in two dimensions. But, the gusset that makes a box liner sit squarely can be used as a third dimension, which makes fitting far easier. To make your measurements, try this quick reference guide for calculating the dimensions you will need for your box liners.
| Box liner size calculator |
| Box Height (H), Width (W), Depth (D) W + D + 4cm = box liner width needed Half D + H = box liner length needed |
Side note; this will also work for pallet covers and gusseted bags, which are similar configurations of polythene.
Instructions
Measure the height (H), width (W) and depth (D) of the box to be lined (depth is the shortest side). Add W to D, plus 4cm for slack. This gives you the opening size, or total bag width. To find the size you need to cover H (which will be the length of the bag), divide D by 2 and add to H, plus 10-15cm for overhang.
| Box liner size calculator example | ||
| Box dimensions (H,W,D) | Calculations | Box liner size needed |
| 40cm x 30cm x 20cm | 30 (W) + 20 (D) + 4 = 54cm 15 (0.5D) + 40 (H) +15 = 70cm | 54cm (W) x 70cm (L) |
Get custom-sized polythene box liners from NPF Packaging
Need help sizing up and ordering your first batch of custom box liners? Get in touch with us now. Contact us or call 01773 820415.