Corrugated Box – The Master Guide

stay of corrugated boards

Corrugated boxes are a highly versatile tool for you and your company. It is possible to use a corrugated box as a primary, secondary, or tertiary packaging solution ranging from regular shipping to custom printed packaging.

What is cardboard made of?

The conventional cardboard box comprises of 3 fiberboard layers in its structure. The outer layers are called linerboards, and the wavy layer of paper sandwiched in between the linerboards is called flute. In some cases, to add extra protection to the products, corrugated sheets can be doubled-up, combining different grades of fluting. 

The everyday corrugated box is the most common as a shipping and mailing option. The walls provide the much-needed protection for even the roughest handling, and the material is relatively cost-effective. Most companies use corrugated boxes to efficiently ship and deliver enormous amounts of products over long distances. In contrast, some companies opt for printing on their corrugated boxes.

Although these boxes are ubiquitous within our everyday lives, little is known about them.

In this post, we discuss everything you need to know related to corrugated packaging.

Types of Paper

Kraft Liners

Manufactured from softwood trees, Kraft paper consists of 70-80% “virgin” chemical pulp fiber, which results in a top paper grade that is very stiff and durable. Kraft paper is the most sustainable option out of all the types of paper. However, Kraft paper is also the most costly option.

  • Brown Kraft may vary in natural brown color depending on the different fibers used, the pulping process, and the location of the paper mill
  • White Top Kraft is very strong and affordable and offers excellent printing characteristics
  • Mottled Kraft aka Oyster Kraft, similar to White Top Kraft with a mottled appearance
  • Fully Bleached White is a Kraft liner with a natural look with an additional bleaching stage but this option is not as durable as the unbleached option
  • Birch Faced Kraft similar materials as White Top Kraft, but the top ply is bleached

Test Liners

Test paper is a less costly option than Kraft. There is a higher percentage of recycled-fiber content, resulting in a less durable paper liner. The higher recycled fiber content also makes the paper more difficult to print. Which makes it very common to use Test paper as the inner linerboard of a corrugated box.

  • Test 2 is partly recycled liner paper
  • Test 3 is fully recycled liner
  • White Top is a white-coated recycled liner
  • Oyster is a mottled test liner

Flute Paper

  • Semi Chem is virgin fibers using neutral sulfite semi-chemical process
  • Waste Based Fluting is 100% recycled fibers

Flutes Grades

Corrugated box fluting refers to the arches in between the linerboard that helps to strengthen material for stacking and durability. These flutes are made of fiberboard, same as the linerboard, and they provide corrugated sheets with strength, cushion, and compression resisting qualities. It also can be potentially used for custom printing and graphics. Fluting comes in various types and each type is unique.

  • Linerboard is the face of the fiberboard sheet that the corrugated sheet is glued on.
  • Single Face is a single corrugated fiberboard that is glued to one flat sheet of linerboard, revealing the fluting on one side.
  • Single Wall is the fluted fiberboard that is glued between two sheets of linerboard. This is the standard corrugated board that we usually see.
  • Double Wall has three sheets of linerboard with two corrugated fiberboards in between.
  • Triple Wall is four sheets of liner board with three corrugated fiberboards in between.

Single Wall

Single-wall corrugated box styles vary in material strength and durability. This can be tested with the Edge Crush Test, as discussed later in this guide.

Single-wall corrugated boxes can carry weights from 23 ECT to up to 55 ECT. It weighs less and “weaker” single-wall corrugated boxes may hold up to a minimum weight of 20 lbs.

A-Flute – 1/4” is the first type of corrugated flute. This flute grade has the highest protection and cushion qualities. Very good at handling compression and stacking, it is often used to package fragile items.

B-Flute – 1/8” this type of flute appears much thinner than others, but do not let its’ appearance fool you. B-Flute is quite strong, and it typically used for counter displays and canned food products. It also has a flatter surface for higher quality printing and is excellent for die-cutting. B-Flute has excellent puncture and crush-resistance properties while also consuming less space. It has excellent all-round performance for all types of packaging, but also commonly used as padding, dividers, partitions, and other forms of inner packing material.

C-Flute – 3/16” is flexible and one of the most versatile flute grade in cardboard boxes. It has average crush resistance, stacking strength, and printing properties. You have likely seen this type used for shipping boxes but also used to package glass, dairy, and furniture products.

E-Flute – 1/16” is not typically used for shipping. As one of the thinner flute grades, E-Flute is often used as an alternative for paperboard folding cartons. E-Flute is also designed thinner and more condensed to reduce the outer box dimensions, which saves on storage space. Although thinner, E-Flute has excellent compression strength, crush resistance, and a relatively flat surface for high-quality printing applications. You may use E-Flute for cosmetics, fragile glass, ceramics, and other small and delicate products.

F-Flute – 1/32” has protective qualities similar to E-Flute but with an even smoother surface for high-quality printing. It is common for you to use F-Flute for clamshell packaging for fast-food chains in the United States. On the other hand, Europe has adopted this grade of corrugated fluting as a standard option for specialty and retail packaging.

Max. Weight Box/Contents (lbs.)Min. Burst Test (lbs. per sq. in)Min. Edge Crush Test (lbs. per in. width)

Double Wall & Triple Wall

Because there are at least two walls of corrugated sheets in this style of corrugated box, double-wall, and triple-wall boxes are, of course, more durable. The downside to this, if applicable, is that the box is less flexible. In some cases, this trait may be necessary for certain products. This type of corrugated box is ideal for shipping and storage, as they are quite durable and can withstand regular wear and tear.

Triple-wall boxes have three stacked corrugated sheets and four liner board facings. Triple-wall corrugated boxes are extremely durable and can typically withstand a maximum of 300 lbs.

Although it is possible to form many different combinations of double-wall or triple-wall corrugated boxes, here are a few standard double-wall combinations found within the industry:

AC Flute is a combination of two most protective corrugated grades. The result is a very strong corrugation used when extra strength is needed. This is an excellent option if you need extra protection from the shipping and handling process. With A-Flute stacking and compression resistance, this combination also makes for an excellent storage option.

BC Flute is an excellent all-round performer, this combination provides high-level transit protection and most often seen in shipping cases.

EB Flute provides excellent transit strength and protection, while the outer E-Flute allows for an excellent high-quality printing surface.

Max. Weight Box/Contents (lbs.)Min. Burst Test (lbs. per sq. in)Min. Edge Crush Test (lbs. per in. width)
(minimum puncture test, oz. per in. of tear)
Max. Weight Box/Contents (lbs.)Min. Burst Test (lbs. per sq. in)Min. Edge Crush Test (lbs. per in. width)

Material Strength Tests

Corrugated boxes are common for shipping and mailing purposes. They are subject to different kinds of stress and impact during the packing, shipping, and storage process. So corrugated material needs to be able to resist damage as much as possible to protect the products inside. There are different ways to test the strength of corrugated material. But which test should you use when selecting material for your corrugated boxes?

Edge Crush Test is one of the essential tests for corrugated packaging material. As the name implies, force is applied perpendicular to the edge of the corrugated board until it buckles. The results provide manufacturers the confidence for the material to have the strength and durability required to handle heavy loads and stack resistance.  The resulting value is shown in pounds per linear inch of load-bearing edge and is reported in ECT ratings. See also Box Maker’s Certificate

32 ECT is the most commonly used for corrugated material. 

Flat Crush Test is similar to the Edge Crush Test. This test applies force directly on a surface area of the corrugated fiberboard until the flute flattens and compromises its structure. This test determines the compression and stacking resistance of the corrugated board required to carry heavy loads.

Burst Test, otherwise known as the Mullen Test, tests the durability of the corrugated fiberboard’s surface. As the Flat Crush Test tests compression resistance, the Burst Test determines the amount of force required to puncture the linerboard. The resulting value is given in pounds per square inch. See also Box Maker’s Certificate

200# means 200 pounds per square inch of force applied to the face of the linerboard. 

Water Absorption Test, otherwise known as the Cobb Test, determines the level of moisture that the material needs to remain below to maintain its structural integrity to protect the product. Measuring the absorbency of the box surface is also important because it may affect the printability of the box. On the back surface, the same test indicates how well the liner will adhere to the fluting. The test begins by setting a sample of the paper material above an open container with a specific measurement of liquid. The container is flipped, allowing liquid to absorb into the material for a certain amount of time before being removed and examined. 

Ring Crush Test measures the compression of paper and board materials. A strip of paperboard with a standardized length and width is formed into a ring. Force is applied perpendicular to the paper’s edge until it buckles. 

Short Span Compression Test has become a popular alternative to the Ring Crush Test. A strip of standard-sized paperboard is placed between a set of compression plates which then clamp onto the paperboard to determine the material’s compressive strength. The test repeats throughout the length of the paperboard to determine the strength and durability of the material.

Box Maker’s Certificate

Have you ever picked up a box from Amazon or Uline, checked the bottom and found a circular stamp that looks like a nutrition facts label? That is a box maker’s certificate, also called a BMC. It is a convenient and efficient way of describing some quick specifications about the box.

There are 2 versions of box maker’s certificates: ECT-Rated BMC and the Mullen-Rated BMC.

There are a couple of visible differences but in essence, these two certificates provide the same information.

Box Manufacturer is indicated in the outer ring. This is the company that is responsible for manufactured your box.

Board Construction is the information displayed directly under where it says box certificate. This information indicates the thickness and construction of the box walls by stating whether the box is single-wall, double-wall, or triple-wall.

Minimum Combined Weight Facings is the total weight of the linerboard used before the full linerboard is cut and made into boxes.

Size Limit is the maximum outer dimensions of the box. This section is useful to know for storage and shipping purposes.

Gross Weight Limit is the maximum weight allowed for the box and the items in it.

City & State is the final information stated on the box at the bottom of the label. This is where the box is made and shipped from.

Know your corrugated boxes, style and dimensions, design, print, and labeling as well as shipping in the US and Canada by your custom box design supplier.

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