Corrugated board consists of two, paper-based flat boards with a wavy, or fluted, layer in the middle. It is commonly used to make strong boxes and shipping containers. Different types are rated using strength tests.
The burst test measurement is stated in pounds per square inch and measures how a box can stand up to internal and external forces against hydraulic pressure. Some types include 200 test, 275 test and 350 double-wall, the strongest. Burst test board is considered stronger and higher quality than boards which have not been tested.
Edge Crush test
The edge crush test (ECT) tests how much pressure is needed to crush a box from top to bottom. A box with 32 ECT means it can stand 32 pounds per square inch without compression.
The outer and inner lining sheets also have grades. Some examples are K (Kraft), made from virgin Kraft paper, T (Test 3) for fully recycled paper, and C (Chip) for waste-based liners.
The fluting in between the liners has a corresponding letter grade. It ranges from A to F with A being the thickest. The most common grades are B and C.
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