Box spec / 6 MIN READ

Same box for 10 years? What it's costing you

The pallet is wrapped, the lorry is booked, and the bottom row of boxes has bowed out like a tired accordion. Someone says it's the weather. Someone else says it's the driver. Rarely does anyone ask the box. Yet the box is the one thing on that pallet nobody has re-checked since the day it was approved.

By KP Trading & Distribution · 6 minute read

Same box for 10 years? What it's costing you, KP Trading and Distribution. Photo is illustrative. — Corrugated box specification review · Photo is illustrative

If you've bought the same box for ten years, the box you get today may not be the box you specified. Board has been made lighter over time, most UK paper now comes from recovered fibre, and your spec sheet may describe something the mill no longer delivers. You can end up paying for a stronger box than you receive, or stacking a weaker one than you think. Both cost money. Neither shows up on the invoice.

Has corrugated board really changed?

Yes. FEFCO, the European corrugated body, says base paper weights have been reduced over time. About 80% of UK-made paper uses recovered paper, according to the Confederation of Paper Industries (2023 figures).

None of that is bad in itself. Not at all. Lighter, well-made board can do the job. The trouble starts when the spec sheet still says what it said in 2016 and nobody has checked what turns up on the dock.

What does 125K/B/125T actually mean?

It's UK shorthand for a board, written outer liner, flute, inner liner. Here 125K is a 125 gsm virgin kraft outer, B is the flute, and 125T is a 125 gsm fully recycled testliner inside.

K means virgin kraft, T2 part-recycled testliner, T fully recycled testliner, SC semi-chemical fluting, WB recycled fluting. Flute letters give thickness: B is about 3mm, C about 4mm, A about 5mm, E 1.5mm and F 1mm. A double wall such as BC runs to about 6mm.

Here's the catch. Two boxes can both say "single wall B flute" and be very different. The difference hides in the grade codes.

Which box tests should you ask for, and what do they catch?

Let's go through them in plain English. For each, we'll say what it catches and what it costs when it goes wrong.

Grammage is the weight of the board per square metre. Component grammage separates the liners and fluting and weighs each one. It catches a lighter liner than the sheet says. Fail it and you're paying for 125 gsm and receiving less. Every sheet, every pallet.

Caliper is thickness. A crushed flute shows as low caliper. It catches damage from rough converting or storage, and the result is a weaker box that looks fine from outside.

Edge crush test (ECT) squeezes a small strip of board on its edge. It's the best single guide to how well the board resists stacking load, and low ECT is where crushed stacks begin.

Box compression test (BCT) crushes a whole box. The McKee formula estimates it from ECT, caliper and box perimeter. That estimate suits empty boxes only, so a filled box still needs testing. Lab BCT isn't a safe stacking load either, and factors of 4 to 5 are often used to turn one into the other.

Burst measures how much pressure the board takes before it ruptures. It catches weak liners, and low burst means punctures, tears and returns.

Flat crush measures how well the fluting resists being squashed flat. It catches weak medium, and the loss shows up as soft, floppy boxes.

Moisture is the water content of the board when it's tested. Wet board is weak board, and results taken at the wrong moisture level are misleading.

Cobb measures how much water the surface takes in over a set time. It tells you about surface absorption, not wet strength or stacking.

Glue bond immersion checks whether the liners stay stuck to the fluting after water exposure. Burst after immersion measures how much strength the board keeps once wet. Fail these and wet boxes delaminate and the stock inside is damaged.

Is a soak test a proper test?

"Soak test" is an informal phrase, not one standard test. When someone says they'll "soak test" your box, ask which method they mean: Cobb (ISO 535), glue bond immersion (ISO 3038), burst after immersion (ISO 3689), or something else.

One thing soaking can't do is tell you the board grade. Wetting a sample won't reveal whether the paper is 125 gsm or 150 gsm. That needs component grammage (ISO 3039).

Test severity should match the box's life too. A soak that suits a chilled-room box is overkill for a dry warehouse.

What does a weaker-than-the-sheet box cost?

Here's what we found. We had samples tested and checked construction, board weight and spec line by line against the supplier's own spec sheet. Every line came back weaker than the sheet.

Say your sheet box is priced at 25p and the box you actually get is worth 21p. That's 4p a box. On 100,000 boxes it's £4,000 you've paid for board you never received. This is an illustrative example, but the arithmetic is real.

That's the quiet cost. It repeats on every order. The loud ones are crushed bottom layers, returns, and damaged stock claims on the day the shortfall surfaces. GWP, a UK packaging distributor, notes that the cost of damaged goods can far outweigh any saving on the box.

Not sure what yours are costing you? We'll check them with you on site.

Is your box over-specified, or under-performing?

Often both, in the same factory. GWP calls over-specification surprisingly common: a heavy grade is chosen to fix a damage problem and never revisited. Go too light and you get transit damage.

Design detail matters as much as grade. DS Smith found that removing 3mm from a case improved pallet fill by 13.3%. The flute direction gave a 24% performance difference between the same trays made at two sites. One redesign cut material use by more than half.

So the answer is rarely "buy heavier". Know what you've got. Know what it has to do. Then match the two.

What about chilled storage and humidity?

Briefly: chilled food must be kept at 8°C or below by law in England, Wales and Northern Ireland, according to the Food Standards Agency. Cold rooms are damp, and fibre swells and weakens as humidity rises.

Georgia Tech research found roughly a 10% loss in edge crush and box compression strength for each 10-point rise in relative humidity. If your boxes live in a chiller, ask for humidity-conditioned compression testing, not just a dry number.

How do you fix your box spec?

Review it. BRCGS Issue 9, as commonly summarised, expects specifications to be reviewed at least every three years. Do it with both the buyer and operations in the room, because they see different halves of the problem.

Write down the grade, the flute, the component grammage, the ECT and the storage conditions. Ask the mill to quote to the spec sheet and again "as supplied". Test samples before you quote, not after the first complaint.

Never swap a box without sign-off from the buyer and operations. A change that saves 2p at the mill can cost you far more on the dock. Re-check at least every three years, and sooner after any supplier change. Put the date in the diary today.

Frequently asked questions

How often should a box specification be reviewed?

At least every three years under BRCGS Issue 9, as commonly summarised, and whenever a supplier, product weight or storage condition changes.

Can a soak test tell me my box grade?

No. Soaking can't identify grade. Component grammage testing separates the liners and fluting and weighs them.

Is a higher burst figure always better?

Not necessarily. Stacking depends mostly on edge crush and box compression, while burst tells you about puncture and tear resistance.

Who should own the box spec?

One named person, working with both buyer and operations, with a calendar date for the next review.

Send us your box and its spec sheet

Send us your current box and its spec sheet. We'll tell you what it really is, what it's costing you and what it should be, and we'll arrange testing where it's needed.

It sits inside our free site check. We walk the site with your operations team for about 30 minutes and send you a written report. No contract.

We compare cost per use, not price per pack, and we never swap a spec without your approval. Every client gets their own login with the spec sheets and certificates for what they buy from us.

Email sales@kptrading.uk or call 020 4576 5500.