Guide to Corrugated Cardboard Thickness Grades - Industrial Physics Guide to Corrugated Cardboard Thickness Grades - Industrial Physics

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Guide to Corrugated Cardboard Thickness Grades

Quickfire guide to corrugated cardboard thickness grades

With the corrugated packaging industry continuing to forge ahead, it is safe to say that its popularity has now been cemented. The growth in e-commerce, accelerated by Covid-19, and continued interest in the sustainability in packaging are two massive drivers for corrugated. This makes now the ideal time to see the benefits corrugated has to offer, in terms of flexibility, strength and affordability. So, let’s explore corrugated board grades.

How is corrugated made?

Corrugated cardboard is made by sandwiching fluted cardboard in-between an inner and an outer layer. Additional layers of liner and corrugation can be applied to up the levels of rigidity and strength.

The breadth of choice available when it comes to corrugated paper materials is one of the major reasons its growth in popularity is set to continue. So how does the breadth of choice factor in when it comes to the components of corrugated cardboard? Here’s a look at the variety of options out there.

Corrugated paper options

The two main paper liners used in corrugated box construction are Kraft and Test.

  • Kraft paper is commonly used as an outside liner. It is made from softwood trees and because it is made from fibers directs from the source, it is particularly strong. These “virgin” fibers also provide a great surface for printing.
  • Test paper is more often used as an inside liner. It is double layered and is often referred to as Duplex paper. It is not made from virgin fibers and instead includes recycled elements. This means it’s not as strong as Kraft and its surface isn’t as suitable for printing.

Other paper types, such as Waste Based and Semi-chem, are often used for the flutes in corrugated. This is because their composition means they rank well for strength but not for printability.

Some of the most common paper types used include:

  • Kraft (K): Virgin Kraft paper
  • Mottled Kraft (MK): Mottled white Kraft
  • Fully Bleached White (BW): Fully bleached Kraft liner
  • Test 2 (T2): Partly recycled liner paper
  • Test 3 (T): Fully recycled liner
  • Chip (C): Waste based liners
  • White Top (WT): White coated recycled liner
  • Mottled Kraft (MK): Mottled white Kraft
  • Oyster (OY): Mottled test liner
  • Semi-chem (SC): Virgin fibers using neutral sulphite semi-chemical process
  • Waste Based (WB) 100% recycled fibers


Flute profiles in corrugated boxes

Flutes are measured both by weight and thickness, both of which relate to the strength and performance of the resulting cardboard.

Flute weights in GSM:

  • 90 GSM WBF
  • 105 GSM WBF (this is the most common flute choice)
  • 112 SC and WBF
  • 150 SC and WBF
  • 175 SC and F

Flute sizes in mm:

  • A FLUTE – 5mm
  • B FLUTE: 3mm (a versatile all-rounder used in all types of packaging)
  • C FLUTE: 3.5-4mm (often used for lightweight products)
  • E FLUTE: 1-1.5mm (very fine and more suitable for printing and small cartons)
  • F FLUTE: 2mm

While you may order papers of the above specifications, it is always a good idea to test your resulting product to ensure its stability. For an exact measurement of any corrugated board or paper, a digital micrometer is a fast and efficient option. Capable of returning results in microns, they are also incredibly precise. A sturdy micrometer ideal for measuring corrugated is the 49-87 Digital Micrometer.

Corrugated testing solutions from Industrial Physics

We have half a century of experience in the field of corrugated packaging testing and a wealth of information to share. We can talk you through every aspect of your setup or advise when it comes to adding just one specific testing solution – whatever suits you best.  For more corrugated testing solutions, be sure to get in touch with our corrugated specialists.