Cardboard. At first, it doesn’t sound like a particularly complex product to get your head around. But how much do you really know about it? B-Flute, F-Flute, Test Paper, Semi-chem. What does 125K/B/125T mean? Corrugated fibre board is a minefield, and it’s not easy to navigate. There are a plethora of options out there when deciding what will be the best option for your product.
If you are using large volumes of packaging, the chances are that you will be familiar with the intricacies of corrugated cardboard. But, for something that we are exposed to everyday, many people pass it by without giving it a moments thought. This guide aims to explain everything you could possibly hope to know about cardboard. Liners, flutes, gsm, it will all become clear. And, hopefully, you will be able to make more educated decisions on packaging choices in the future.
How is it made?
Let’s start at the very beginning before we start to discuss the technical details. The most basic form of cardboard that you can get hold of is composed of three elements, a layer of ‘fluted’ material, placed between two layers of paper, referred to as the inner and outer liners. The center fluted sheet is glued to the two liners during manufacture, which adds rigidity and stability to the board.
The types of papers
The main factor in defining the properties and application of corrugated material is the type of paper that is used. The two main types that you may be familiar with are Kraft and Test liners.
Kraft paper is the most commonly used outside liner when selecting materials to produce corrugated boxes and packaging. It is manufactured from softwood trees. Because of its ‘Virgin’ fibres, it is the strongest type of paper to use in the manufacture of cardboard. It is also the easiest to print on. ‘Virgin’, as you may have guessed, refers to pure, unrecycled paper straight from the source. This is regarded as stronger as recycled paper tends to degrade after several uses. There has been a huge push recently for the paper and packaging industry to source fresh fibre from responsibly managed forests to keep the renewable cycle going as we now recycle over 75% of our paper!
Test paper is a double layered, otherwise referred to as ‘duplex’, paper. Duplex paper is not a virgin stock, therefore it is not as strong as Kraft, and it’s not as easy to print custom branding onto. As a result of these attributes, it is commonly used as an inside liner. These pitfalls in quality result in Test paper being much less costly than Kraft.
Each liner type is composed of two layers. A basic layer is used to provide adhesion and strength whilst another finer ‘cover’ layer is used to improve aesthetics and to aid printing.
Test and Kraft paper options are the most popular types of stock used in the manufacture of cardboard, however, there are many other alternatives when designing your packaging.
Kraft (K): Virgin Kraft paper
Test 2 (T2): Partly recycled liner paper
Test 3 (T): Fully recycled liner
Chip (C): Waste based liners
Fully Bleached White (BW): Fully bleached Kraft liner
White Top (WT): White coated recycled liner
Mottled Kraft (MK): Mottled white Kraft
Oyster (OY): Mottled test liner
Semi-chem (SC): Virgin fibres using neutral sulphite semi-chemical process
Waste Based (WB) 100% recycled fibres
Waste based and Semi-chem are most commonly used for the flutes and not usually used as liners, this is because they offer strength but are not able to be printed on.
This list only mentions a few other alternatives to Kraft and Test paper, the market is flooded with even more options than the ones listed.
Paper Weights and Grams per Square Meter (GSM)
Once the types of paper available are understood the weight of the paper should then be considered. The standardised measurement used throughout the paper and packaging industry is Grams per Square Meter (GSM). This is used to determine the weight of the stock in everything from cardboard to copier paper to folding box board. It is simply how much a square meter of the material would weigh in grams.
If you were using a corrugated board that has a 150gsm Kraft paper liner, this will be expressed as ‘150K’. There are a range of common, standard paper weights that are used for corrugated material. These include:
- 115/125 gsm
- 140/150 gsm
- 185/200 gsm
- 250 gsm
- 300 gsm
Although, there is an extremely wide variety of gsm grades available.
Types of wall
As mentioned earlier, in its most basic form, cardboard is comprised of two liners and a fluted centre. This is commonly referred to as ‘Single Wall’ board. Although this is the standard for cardboard, it can be quite easily bent along the fluting and it isn’t a heavy-duty option.
To combat this problem, an additional fluting section and another liner can be introduced. This is known as ‘Double Walled’ material. It adds rigidity and strength that singled walled material simply can’t offer. It also acts as an extra buffer zone, so when, inevitably, your box gets thrown around in transit there is a higher degree of impact resistance. Double walled materials are also more suitable for housing heavier items which may otherwise wear down, or tear through a single walled box.
You can add an extra wall. It’s as simple as adding another liner and an extra layer of fluting. This is only used for particularly expensive items, or items which need an extremely high level of protection. It’s known as ‘Triple Walled’ or Tri-Wall, which has become a genericised trademark and there are many manufacturers that produce triple walled products.
You don’t have to stop there, either. There are a variety of companies that produce ‘Quadruple Wall’ (QW) cardboard sheets. However, these are reserved for extremely specialist projects and are extremely rare within the packaging industry.
Types of Fluting
The final aspect of cardboard that can affect its price and performance is the type of fluting that is used. It is possible to change the height and the density of the flutes to change the cardboard’s applications and performance. At the very bottom of the scale you have ‘E’ flutes which is used for lightweight retail cartons, and due to the flute density, is very good to print onto. And, at the top of the scale you can use a much coarser flute such as an ‘A’ or ‘B’ flute, which is usually reserved for transit packaging.
If you want to offer greater protection and a much more rigid structure, you can combine types of flutes to produce ‘Double Walled’ cardboard sheets. For example, ‘EB’ flute or ‘BC’ flute. This only offers greater structural integrity, but you can improve bespoke print quality if you use the finer flute on the outside of the carton.
As mentioned earlier, the flute itself tends to be manufactured from a waste-based material/ fully recycled material. As it isn’t integral for the flute to look good or be printed onto. The most common variants of paper weights to be used for fluting are:
- 90 GSM WBF
- 105 GSM WBF – Most Common Flute Standard
- 112 SC and WBF
- 150 SC and WBF
- 175 SC and F
There are also a number of commonly used flute profiles and sizes, which are:
- A FLUTE – 5mm
- B FLUTE: 3mm
- C FLUTE: 4mm
- E FLUTE: 1.5mm
- F FLUTE:.2mm
- BC FLUTE: Double Wall – 6mm -Combination of B + C flutes
- EB FLUTE: Double Wall – 4.5mm -Combination of E + B flutes
These are the standardised types of flute sizes, but manufactures tend to make extremely similar products and give them brand names, which can make navigating the market quite complex as the names are entirely exclusive to that manufacturer.
Shorthand cardboard descriptions + Flute breakdown
Now you are armed with all this information, you are able to create a shorthand abbreviation that describes the type of board being used in a concise fashion.
For example, if the material grade was using a 150gsm Kraft outer liner, a 150gsm Test inner liner and E fluting, this could be expressed as:
150K/E/150T
This is an industry-wide method of expressing the grade of material you want your cardboard to be composed of. Virtually anyone in the packaging industry will recognise it.
E flute
E flute is approximately 1mm to 1.5mm in thickness, this means it is an extremely fine flute. It is very resistant to crushing and compression and provides a high quality, smooth surface for printing. E flute would not be appropriate in a single-walled carton to hold weighty products, due to its size. It is mostly used for printed retail cartons.
E flute has around 90 flutes per foot.
B flute
B flute is maybe the most commonly used cardboard fluting in the world. It is 3mm in thickness and is extremely versatile. It can be used in die cutting and regular case-making processes. It simply offers good all-round performance in all types of packaging.
B-flute typically contains 47 flutes per foot and has a thickness of 1/8th”
C Flute
C flute tends to fall between 3.5mm and 4mm in thickness, C flute improved compression strength against B flute due to its thicker gauge. The benefit of this is that it can be stacked much higher than B flute cartons and can house lightweight products.
C flute has around 39 flutes per square foot and a thickness of 3/16th”
BC Flute
Being between 6mm and 7mm in thickness, this is a double walled container combining B and C fluting. The most common applications for a cardboard such as this is transit boxes/ shipping boxes and items that require a higher level of transit protection. BC flute is most commonly printed on using a method such as flexographic, or flexo print.
EB Flute
EB flute is about 4mm to 4.5mm thick. And as you would assume, it is a mixture of E and B fluted material to, again, form a double walled material. The internal wall provides very good transit protection whilst the outside, finer grade, provides a great print surface.
In Summary:
Hopefully this information has helped you begin to understand the seemingly complex minefield of corrugated packaging. Once you have got your head around the industry-specific terminology, it’s easy to navigate.