Technical Explanation of Corrugated Board

1. Understanding Corrugated Board

A blue standard sheet of corrugated board is made from three components: a sheet of corrugated fluted paper, sandwiched between an outside liner
and an inside liner.


2. Types of Paper

The basic material for the production of corrugated board is paperboard. There are two main types of paperboard:

  • Kraft Paper –  Comes from softwood trees and is the strongest form of paper and the best to print on. This is the most common outside liner for corrugated boxes.
  • Test Paper – This is a so-called double layer paperboard (duplex paper). Most standard cartons use recycled paper for the fluting and the inside liner. Each sheet of liner paper is commonly composed of two layers. The finer cover layer is ideal for printing and aesthetics, and the basic layer is excellent for adhesion and strength.


3. Paper Weight

After understanding the paper type, the next thing to look at is the thickness. This is measured the same way for all papers.


Take one square meter of your paper and weigh it. The result is XX grams per square meter (which is abbreviated to gsm). E.g. photocopy paper = 80gsm


4. Corrugated Walls

So far, we have looked at corrugated board made from a single fluting with two liners. This is referred to as single wall. However, an additional fluting and wall can be glued together to make a stronger board, called double wall. This is suitable for packing heavier goods. If you need to package extremely large and heavy items (for example, large machine parts), triple wall boxes can be used. This adds yet another fluting and liner.


5. Common Flute Sizes

Corrugated board has five common sizes of fluting, ‘A’, ‘B’, ‘C’, ‘E’ and ‘F’. The letter designation refers to the order they were invented, not their relative size.


A = 5mm fluting
C = 4mm fluting
B = 3mm fluting
E = 2mm fluting
F = 1mm fluting


Double wall cartons can use combinations flute sizes.


6. Board Grade Explanation

Combining all of the above, it is possible to specify a simple short description that defines the board grade of a box. For example: 125K/B/125T. This means a corrugated box, made from 125gsm Kraft outer liner, B fluting and 125gsm Test inner lining.


Corrugated Stock Boxes – 32 ECT versus 200# Test

For many years, the corrugated industry has maintained two standards for measuring the strength of corrugated board, which sometimes leads to confusion. The Mullen Test, which measures the bursting strength of corrugated board, has been in existence for many years. The Edge Crush Test, which measures the stacking strength of corrugated board, became popular within the last ten or fifteen years.


In most cases, 200# Test (Mullen Test) and 32 ECT (Edge Crush Test) perform equally well. For stock corrugated boxes, stacking strength is usually more important than bursting strength, which is one reason why most of our stock boxes conform to the Edge Crush standard. A second reason is cost. Slightly less linerboard is required to manufacture 32 ECT corrugated boxes than the 200# test equivalent.