Corrugated Cardboard Grades and Thickness
Two main factors determine your corrugated cardboard boxes’ strength and compression resistance:
- Containerboard Grade
- Containerboard Thickness
Corrugated Containerboard Makeup
First, let’s define corrugate. Corrugated boxes are made of:
- Flat linerboards
- Fluted media
The linerboard and fluted medium are glued or bonded together. The linerboard and the fluted medium are made of a sturdy kraft paper called containerboard.
Board grades and thickness are not identical.
Corrugated Board Grades
Corrugated board grade refers to the containerboard’s construction, including the number of linerboard layers and fluted media glued together.
These grades help establish the strength of the containerboard.
Corrugated board grades include:
- Single-face boards
- Single-wall containerboards
- Double-wall containerboards
- Triple-wall boards
Illustrations of Four Board Grades
Single-face Boards
A single-face containerboard includes one flat linerboard bonded to one fluted medium. It can be likened to an open-face sandwich.
Single-wall Containerboard
By contrast, a single-wall containerboard comprises a fluted medium sandwiched between two paperboards. It’s a typical sandwich made with a fluted filling and two slices of containerboard bread.
Double-wall Containerboard
The double-wall containerboard has two fluted media and three flat linerboards. Think of it as two hamburger patties (fluted media) sandwiched with an added piece of bread (linerboard) in the center. In other words, it’s a five-ply structure.
Triple-wall Containerboard
Triple-wall containerboard has a seven-ply structure: three layers of fluted media sandwiched between four containerboards. Triple-wall containerboard is less common but extremely strong. You can ship watermelon in a triple-wall box.
Why Board Grade Matters: Strength
Board grade determines the strength of a box. The more layers, the stronger the box. For most purposes, a typical single-wall corrugate can support items.
Similarly, a single-face grade may provide enough strength for exceptionally light items.
However, a stronger board grade is usually required when an item is fragile.
The number of items and the total weight of packed items will also affect the corrugated board grade you need. At times, shipping fewer items per box may be less expensive, reducing both shipping costs per box and the grade of containerboard needed.
Board Thickness (Flutes)
Board thickness refers to the thickness of the fluted media used to make the corrugate—the meat inside the sandwich.
Board thickness is measured in millimeters or inches and varies by flute type. Board thickness or flutes are represented by letters: A, B, C, E, and F.
Different flute types (A, B, C, E, and F) have varying thicknesses. “A Flute” is the thickest; “F Flute” is the thinnest fluted medium.
A Flute
“A” Flute is the thickest flute. It typically measures 5mm (~ 1/4 inch to 3/16 inch thick). It provides the most cushioning for fragile products. It is stiff and crush-resistant and has 33 flutes per foot.
B Flute
B Flute is about 3mm (1/8 inch thick). It allows for die cuts with sharp, crisp edges. It is puncture- and crush-resistant. B Flute works well in automated production lines and for interior pads, partitions, and dividers. It has 47 flutes per foot.
C Flute
C Flute is 3.2mm to 4.2mm (approximately 11/64 inch to 3/16th inch thickness). C Flute balances cushioning needs and stacking strength. It is used in many industries, including shipping and food packaging. It is also used in retail displays. This is the type of flute that is typically used in regular slotted containers (RSCs). It has approximately 40 flutes per foot.
E Flute
E Flute is 1mm to 1.5mm (about 1/32 to 1/16 inch thick). A smoother flute, it facilitates high-quality printing. It can be used for folder boxes instead of chipboard or paperboard boxes. A thinner board, E Flute boxes save storage space and can be used for cosmetics, delicate items, and fragile products. E Flute has 90 flutes per foot.
F Flute
F Flute is the thinnest of the corrugated flutes. It measures about 0.8mm (1/32 inch thick). It makes a more rigid box and has 125 flutes per foot.
Downtrodden D Flute
We purposefully did not include D Flute. Although it does exist, it’s rarely used.
Combinations of Flutes
To complicate matters, a double-wall containerboard often combines two different thicknesses of fluted media.
E-B Flute
For example, EB-Flutes (image top) are also commonly used in combination to create 4mm to 4.5mm (approximately 3/16 inch thick) boards. These are excellent for shipping heavy items. Additionally, the E Flute side is smoother, facilitating the printing of high-quality graphics.
B-C Flute
Additionally, we create double-wall containers with B and C flutes (lower image) for a 1/4-inch thickness. This B-C double wall makes a sturdy box that’s suitable for bulky and heavy items, such as paint cans.
Why Flute Type (Thickness) Matters: Cushioning, Resilience, Printing, and Die Cuts
The thickness of the flute determines the box’s cushioning and resilience. These are important when boxes require stacking or durability during delivery.
The flute also affects the appearance of printing on the box. A box with more flutes per foot is flatter, resulting in higher-quality printing. Likewise, die cuts are smoother on a stiffer flute, such as B Flute. Die cuts can create handles, form curved corners, and cut interlocking tabs.
Summary
Grade determines the number of layers and overall strength of the box. At the same time, thickness is the physical measurement of the flute size, which impacts compression resistance, smoothness for printing, and cushioning. Additionally, the type of box you use will also govern the corrugate grade and thickness for your custom boxes.
However, box type, board grade, and board thickness aren’t the only box considerations. Consider a box company’s reputation and production quality. Download 17 Key Corrugated Considerations.
The corrugated experts at Wertheimer Box will help you choose the optimal containerboard grade and flute size for your specific needs.
Get In Touch
Wertheimer Box Corp.
Location
7950 Joliet Rd #100
McCook, IL 60525
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