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How Strong Is Corrugated Cardboard?

The strength of corrugated cardboard depends on its composition. Corrugated cardboard is designed to provide strength and protect whatever it is holding inside. It is available in a number of different grades with varying paper weights and finishes depending on the requirements of the end user. Some types offer exceptional strength and rigidity and support high stacking during transportation, whereas other lighter or narrower fluting grades are suitable for displaying products in retail. The strength of corrugated cardboard packaging starts with its components and how they are combined; there are three main characteristics to consider, the type of paper used, the weight of the paper and the type of fluting.

Corrugated Board Grades

When shopping for suitable packaging for specific products, determining the right board grade is key, it is necessary to be able to understand your product, load weight, fragility, how it will be distributed to your customers etc.. to make an informed decision. The standardised measurement for paper throughout the packaging industry is in grams per square metre (GSM), this applies to all types of paper whether it be corrugated cardboard or simple office copy paper.

The Type of Paper Used

The two main types of paper used to make cardboard products are kraft paper and test paper – the latter may also be referred to as test liners. Kraft paper is the most popular type of paper, it is easy to print on and is also the strongest, due to its virgin fibre content. The virgin fibres are typically harvested from sustainable softwood forests, with the remainder of the composition of kraft paper, usually made from recycled content.

Test paper is not quite as strong and is composed of double layers but does not contain the virgin fibres and does not support printing as well as kraft paper.

What Is Corrugated Cardboard?

In its most basic form, corrugated cardboard consists of multiple layers, an outer layer of paper (this is usually made from kraft paper), middle layer(s) of paper folded into waves known as fluting, then an inner layer of paper.


The most basic form of cardboard is known as single-walled corrugated cardboard, this is not however, the most robust. Stronger types of corrugated cardboard are double-walled and triple-walled – double-walled has an additional fluting section and liner, this adds greater rigidity and strength, and if the box is thrown around, there is improved impact resistance, making it better suited for high stacking and resisting puncture. The strength of corrugated packaging is relative to its density – typically, the more walls a box has, the more robust it will be and the greater the protection it will offer.

Another wall can be added to produce triple-walled, this adds an extremely high level of protection and is often used for breakables and other fragile items.

Fluting Standards

There are also a variety of different types of fluting which will provide varying levels of strength. Fluting is typically graded as follows:

A – Offering approximately 5mm thickness, A-grade fluting offers robust and heavy weight packaging.

B – Possibly the most common type of fluting with approximately 3mm thickness, B-grade fluting is highly versatile and used across the packaging industry. It is often used in die cutting and boxes – offering good all-round, versatile performance across all types of packaging.

C – This type of fluting is thicker than B grade and is typically between 3.5mm and 4mm in thickness, providing improved compression strength.

E – E-grade fluting is a fine type of fluting offering a high-quality smooth surface for printing. It is often used for printed retail cartons.

BC – A double-walled container which combines B and C fluting of approximately 6-7mm in thickness. This type of corrugated cardboard is often used for applications during transit, such as shipping boxes, where greater strength and a higher level of protection is needed. A method of printing known as flexo print is most commonly used on these types of boxes.

EB – A combination of E and B fluted material which forms double-walled corrugated cardboard of approximately 4 to 4.5mm thickness with a smoother, finer grade exterior print surface.

Understanding Standard Strength Ratings

Within the packaging industry, there are standard ways of labelling strength ratings, for example, a corrugated board which has 100GSM kraft paper would previously be labelled as 100K and 100GSM of test paper, previously labelled as 100T. There are some manufacturers, however, that make similar products but give them different brand names.

In the packaging industry an example of a universally understood method of describing the strength of the corrugated board is as follows: 150K/E/150T – this means that the components of the corrugated cardboard include, 150 GSM performance equivalent of kraft paper outliner, E grade fluting and 150GSM performance equivalent of test paper inner lining.

How We Can Help

Nuttall Packaging is an independently owned organisation which specialises in the design and manufacture of corrugated cardboard packaging solutions. We started trading back in 1920 and have been supplying a wide range of boxes for a variety of different clients right across the UK. For more information get in touch today.


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