Corrugated board grades

With 5 Billion corrugated cartons circulating in the UK every year, we are never far from them. When in the supermarket, look out for corrugated trays for fruit, vegetables as well as outers for almost everything displayed on the shelves. In the home, most households these days receive deliveries from online retailers and huge volumes are received and despatched by businesses of every type. But how do you decide on what board grade will work best for the products you’re despatching? Let’s take a closer look at the different protection capabilities, or flutes, of the humble box.

Surely a box is a box is a box?

You might think so but, if so, why do some cartons feel extra-light (or extra heavy?) And some feel ‘soft’ while others feel ‘rigid’? How can one box absorb water and another repel it? Experts in packaging can ensure that boxes will be supplied time and again to perform to a certain standard, using a set of codes that pinpoint which of the variables need to be selected in order to produce a carton that will meet your specific criteria.

What criteria is relevant for deciding on board grades?

As with so many decisions in life, we end up with a trade-off or compromise between what we would like and what we can afford. If not, there might only be a couple of automobile manufacturers to choose from or a couple of retailers. As a simple example, you can reduce the weight of cardboard (and/or the dimensions) with a view to saving money, but the revised box must not jeopardise the safe arrival of the contents!

Demystifying the board grade codes

So what does 125/125 KTBC 457 x 305 x 305mm mean to you? It’s a popular size of rectangular carton that can accommodate A3-sized items and may be useful when moving house and combining a number of smaller items.  And in what way will it differ from a 180/180 KTC of the same size? Starting with the dimensions, they are expressed as Length x Breadth x Height (or Depth) and denote the internal capacity.

The prefixed digits relate to the weight of paper used in grammes per square metre or GSM. The higher the number, the stronger the construction will generally be and the more will be the cost.  Unlike polythene, paper cannot be stated in terms of thickness because papers can -and do -vary in density. This figure will give the first clue to the strength of the board and is known as the board grade and may be expressed as follows: 115/125 GSM; 140/150 GSM; 185/200 GSM; 300 GSM.

Paper Types

After paper weight, then the first capital letter, in this case K, stands for Kraft paper which makes the outer layer of the corrugated sandwich. It is resilient and usually consists of pure virgin softwood fibres in the pulp mix. These fibres are long and bond together strongly. Occasionally there may be a small percentage of recycled fibres added which are inevitably shorter. Kraft is naturally brown and will print up nicely, while white Kraft is the same pulp that has been through a bleaching process and makes the best medium for colour printing.

T for Test

The next capital refers to the other side of the sandwich which becomes the inside of the box. In this case it is T which stands for Test. This is made from something near to 100% recycled pulp and is a 2-ply layer bonded together. It is soft and cheap, but not very strong. The short fibres cannot make a good bond, but the sheet serves as cushioning and works well in this role. Where a box is required to have great strength and rigidity, then both sheets could be made from Kraft.

On the other hand, where price is paramount and the contents are not unduly heavy or sharp, then the construction could be Test/Test and can boast the environmental benefit of almost entirely recycled content. All of this needs to be considered when selecting the correct board grade for your products.

Flutes made easy

Corrugated board flutes

Corrugated board flutes

The fluting size comes next and may be one or two letters depending on whether the construction is single wall or double wall. The fluting is glued in as the filling of the sandwich using high speed machinery. It makes for the strength and rigidity of the board’s construction and is itself available in different weights of paper.




Single Flute Board Profile

Single wall flute board profileFor where the contents are lighter and/or non-fragile.

Double wall flute board profile

Double wall flute board profile

For medium-heavy consignments and where the goods will be stacked on top of each other. Both flutes are identical.

Triple Wall Flute Board Profile

Triple Wall Flute Board Profile

For the heaviest contents and strongest of boxes and sheets


BC flute board profile

BC flute board profile

A popular configuration for price and strength.

EB flute board profile

EB flute board profile

Mostly used in smart retail packaging with smooth, sealed white surface and able to support full colour printing.

What next on choosing a board grades and flute?

Hopefully this guide has provided answers to questions you may have had regarding board grades and flutes.

However, should you have any other questions, or would like to see if you can improve your packaging  – please don’t hesitate to contact Acopia. We’d be happy to talk through a solution for you.

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