Standard cardboard boxes have been in use for over two centuries. The fluted corrugation process began during the first industrial revolution. Since then, corrugated boxes have become the primary shipping containers, essential for all aspects of logistics and material handling.

Chapter Two – How Corrugated Boxes Are Made

While corrugated box manufacturing may seem simple, several critical factors must be considered before production begins. Like all packaging materials used for shipping and storage, corrugated boxes are carefully designed to determine their capacity, stacking strength, shipping durability, and printing compatibility. Optimizing these features ensures reliable performance throughout supply chains, retail, and e-commerce fulfillment.

The first step in producing corrugated packaging involves evaluating key elements: box construction, flute profile, burst strength (Mullen Test), edge crush strength (ECT), flat crush strength, basis weight, paper weight, and coatings. These factors affect not only the box's protective qualities but also its suitability for specific industries—from food packaging to electronics—and its recyclability and cost-effectiveness.

The important Elements of a Corrugated Box

Corrugated Box Construction

Corrugated boxes come in three wall configurations: single-wall, double-wall, or triple-wall. The wall design directly impacts the box's load-bearing capacity and crush resistance, making the right choice crucial for optimal performance and shipping compliance.

• Single Wall - The simplest and most common design, featuring one outer layer, one inner layer, and a fluted middle layer. Single-wall boxes are widely used for lightweight shipping, retail packaging, and product displays due to their affordability and versatility.

  
  

• Double Wall - This design adds an extra layer of fluting and liners, creating boxes suitable for heavier or fragile items. Double-wall boxes offer improved crush and puncture resistance, making them ideal for industrial packaging, electronics, and long-distance shipping.

  
  

• Triple Wall - Featuring three flute layers separated by four liners, triple-wall boxes provide maximum stability and compression strength. They're commonly used for shipping heavy machinery, automotive parts, and other high-value items requiring superior protection.

  
  

Corrugated Flutes

Corrugated boxes typically use one of five standard flute types: A, B, C, E, and F. Manufacturers can also create custom flute profiles by combining standard types or developing unique geometries to optimize cushioning, stacking strength, and printability for specific applications.

• A – The original flute type (36 flutes per foot) offers excellent cushioning and stacking strength, ideal for fragile items and high-compression uses.
• B – With 49 flutes per foot, this type provides strong stacking strength and crush resistance, commonly used for canned goods and pharmaceuticals.
• C – The most common flute (41 flutes per foot) balances cushioning, stacking, and printing properties, making it versatile for standard shipping and retail packaging.
• E – Featuring 90 flutes per foot, this eco-friendly option offers a thinner profile while maintaining rigidity and printability for retail and lightweight shipping.
• F – With 128 flutes per foot, this small, tight flute is environmentally friendly and often used for custom-printed packaging, displays, and food packaging.

Specialty flutes like EE, EF, and BC are used in double-wall profiles for enhanced strength. Rare flutes like N and O (less than 0.5mm height) are sometimes used in micro-packaging and specialty retail applications.

Choosing the right flute type is crucial as it affects shipping performance, cost, print quality, and sustainability. Consult a packaging expert to select the best option for your needs.

Mullen Test (Burst Strength)

The Mullen Test measures how much force corrugated material can withstand before rupturing. Developed over 130 years ago, this test applies force until the material bursts, with results given in pounds per square inch. For example, a 200# rating means the material can handle 200 psi (90 kg). This test helps assess puncture resistance and damage prevention during handling and shipping.

However, the Mullen Test doesn't account for the fluted medium's contribution to stacking strength, which is why the Edge Crush Test (ECT) is also important.

Edge Crush Test (ECT)

The ECT measures a box's vertical compression strength, indicating how well it will hold up when stacked or shipped. This performance-based test is now the preferred metric for most North American shipping boxes. Factors like humidity, storage time, and pallet stacking patterns can affect ECT ratings.

For example, a 55 ECT box can withstand 55 psi (25 kg) before collapsing. Common ratings like 32 ECT, 44 ECT, and 55 ECT help buyers choose the right box for their needs, reducing damages and returns.

Basis Weight

Basis weight refers to the weight of raw cardboard sheets before conversion into boxes, measured in pounds per ream (typically 500 sheets). Higher basis weights generally indicate stronger boxes suitable for heavy-duty applications.

Paper Weight

Paper weight is determined by liner and fluting medium thickness, typically ranging from 26 to 42 lbs (11.8 to 19 kg). Understanding this helps balance cost, sustainability, and protection.

Coatings

Various coatings enhance durability, moisture resistance, and appearance:

• Aqueous - A clear, fast-drying coating offering moisture and abrasion resistance, commonly used for consumer packaging and food-safe cartons.