Corrugated cardboard – what is it and how is it constructed?

Corrugated cardboard is one of the most important packaging materials in the world. It owes its popularity to a unique combination of lightness and high mechanical strength. It consists of alternating bonded layers: smooth sheets of paper (known as liners) and layers formed into characteristic waves.
It is this corrugated structure (the “flute”) that acts as a natural shock absorber—absorbing shocks, impacts, and pressure—thereby providing excellent protection for the contents against damage.

Types of corrugated cardboard (by number of layers)

Depending on the weight or fragility of the items to be packed, cardboard with varying numbers of layers is used:
  • Double-layer (2-layer) cardboard: Consists of one liner layer and one fluted layer. It is flexible, bends easily, and is most often used as protective material (e.g., wrapping for furniture or glass during transport) or as cushioning inside other boxes.
  • Triple-layer (3-layer) cardboard: Features two flat liners and one fluted layer in the middle. This is the most popular type of cardboard, used to manufacture standard flap boxes and die-cut boxes for the everyday shipping of lighter goods.
  • Five-layer (5-layer) cardboard: Consists of two fluted layers and three liner layers. It is very thick and durable, designed for packing heavy products, household appliances, or for pallet transport.
  • Seven-layer (7-layer) cardboard: The strongest variety, consisting of three fluted layers. Used in heavy industry as an alternative to wooden crates.

Flute types (letter designations)

The height and density of the flutes in the cardboard are designated by letters of the alphabet. Each flute type has different properties:
  • E-flute (so-called micro-flute): Low (approx. 1.1–1.6 mm) but very dense. It provides an excellent printing surface and is used for smaller, aesthetically pleasing boxes (e.g., for cosmetics or electronics).
  • B-flute: Low profile (approx. 2.1–2.9 mm). Resistant to flat crush; frequently used for die-cut boxes.
  • C-flute: Medium profile (approx. 3.5–4.2 mm). The most popular general-purpose flute; provides good cushioning.
  • BC-flute: A combination of B- and C-flutes in double-wall (five-layer) board, ensuring maximum strength.

Why is corrugated cardboard so popular?

  • Excellent cushioning: Protects fragile and delicate items from the impact of drops or shocks.
  • Lightweight: Does not significantly increase shipment weight, thereby lowering transport costs.
  • Eco-friendly: Made primarily from recycled paper; 100% biodegradable and fully recyclable.
  • Versatility: Can be easily cut, creased (folded), and adapted to almost any shape.