Packaging listings are full of terms that nobody outside the trade actually uses. E-flute. Single wall. 2-ply. 70gsm. If you have ever scrolled a product page wondering whether any of it matters to your business, here is the plain English version.
It does matter, though probably not for the reason you would guess. The material decides three things: how much protection your product gets, what the parcel weighs and measures (and therefore what you pay to post it), and how your artwork looks once it is printed. Get the material right and every other decision gets easier.
What a "flute" actually is
Pick up an offcut of a cardboard box and look at the cut edge. There is a wavy layer of paper sandwiched between two flat sheets. That wave is the flute, and it is the whole reason cardboard works at all. The waves behave like a row of tiny arches, so the board resists crushing far better than the same weight of flat paper ever could. The flat outer sheets are called liners, and they are the surface your printing lands on.
Flutes come in different sizes, and each size is given a letter. Coarser flutes make thicker, more cushioning board. Finer flutes make thinner board with a smoother, flatter face. The letters are historic rather than logical, which is why nobody can ever remember the order.
E-flute, and why our boxes use it
Our printed postal boxes are made from E-flute corrugated board at 1.6mm thick. E-flute sits at the finer end of the scale, and that buys you two useful things at once.
The first is a flat, even printing surface. Coarse board has a visible ripple running across the face, and printing over a ripple is a bit like painting a fence: fine from across the room, less convincing up close. E-flute gives a much smoother liner, so fine detail and small type hold together.
The second is postage. Thinner board means a finished box with less wall depth and less weight. When your carrier prices by size band, a few millimetres either side of a threshold can move you into a cheaper bracket, which is exactly the sort of thing we covered in our guide to Royal Mail PiP sizes.
Single wall versus double wall
Single wall simply means one layer of fluting between two liners. That is what the vast majority of e-commerce parcels use, and it is what our box range is built on. Double wall is two flutes plus two extra liners, and it exists for heavy, dense or industrial goods.
Double wall is stronger, but it is also thicker, heavier and more expensive to post. If you are shipping clothing, cosmetics, prints, candles, food or small homeware, single wall is the right answer, and double wall is money spent protecting against a risk you do not have. The honest way to decide is not to guess from a spec table but to pack your actual product into the actual box and see how it behaves.
2-ply, gsm and the paper products
Paper is measured differently again. "gsm" is grams per square metre: how heavy the paper is per unit of area, and a fair proxy for how substantial it feels in the hand. "Ply" is how many layers of that paper have been bonded together.
Our heavy duty paper mailing bags are 2-ply 70gsm. Two bonded layers rather than one is what turns a paper bag into something you can trust in the postal network. It resists tearing, and if the outer layer gets scuffed in transit the inner layer is still doing its job. Our paper carrier bags sit in the 70 to 100gsm brown kraft range, which is the sweet spot between a bag that feels flimsy and one that is needlessly stiff and costly to produce.
What the material does to your artwork
This is the part most people find out too late. We print full colour, water-based digital inkjet directly onto pre-manufactured stock packaging, in pre-defined print areas on each product. We are not printing onto a blank sheet of gloss art paper. We are printing onto a real, textured, slightly uneven kraft surface, and the material changes the result.
Three things follow from that:
- Brown kraft warms and darkens every colour. A crisp blue on screen reads as a deeper, earthier blue on the board. The effect is more pronounced on brown and manila than on white stock.
- There is no white ink. Anything white in your artwork simply shows as the bare material, so on brown kraft "white" becomes brown.
- Large areas of solid block colour are best avoided, because they print inconsistently across a textured surface. We go into the reasons and the workarounds in our article on solid block colour on kraft.
None of that is a problem once you know it up front. Line art, outlined type and open, uncluttered designs suit these materials extremely well, and they tend to be cheaper and faster to produce than heavy coverage anyway.
A word on tolerance
Stock packaging is manufactured to a tolerance of roughly 10 to 20mm either way. For most products that is completely irrelevant. If your item is a tight fit, or you are working to a specific carrier size band, it matters a great deal. The sensible move is to order a blank sample and measure it against the real thing before you commit to a print run.
So which do you actually need?
For most UK sellers the answer is unglamorous. Single wall E-flute boxes for anything with shape, weight or fragility. 2-ply paper mailing bags for soft, non-fragile goods where you want to save weight and space. Kraft carrier bags for handing an order over at a counter, market stall or event.
If you are still not sure, do not spec it from a table. A blank sample costs a few pence, and you can hold it, pack it and post it before a single thing is printed. We walk through that process in our guide to ordering a packaging sample, and there are more material and print answers on our FAQ page.
