What exactly is corrugated cardboard?
Corrugated cardboard — also called fluted cardboard or corrugated fiberboard — is made of two or more sheets of paper (called "liners") glued to an intermediate wavy sheet. The corrugations form interconnected arches that act like small columns: they distribute pressure and absorb impacts.
It seems simple, but this arch engineering is what allows a cardboard box weighing less than 500 grams to support 20 or 30 kilos of weight on top.
The air trapped in the corrugations also has an extra function: it acts as a thermal insulator. This is why corrugated cardboard provides reasonably good protection against temperature changes during transport — something that matters if you ship heat-sensitive products.
Flute types: the wave that makes the difference
The "flute" is the inner wave of the cardboard. Its thickness and the density of the corrugations change its strength, cushioning, and ideal use. These are the types you will find:
| Flute | Thickness | Waves/m | What it provides | Main use |
|---|---|---|---|---|
| A-flute | ~5 mm | 105-125 | Maximum cushioning — absorbs strong impacts | Moving boxes, fragile products |
| B-flute | ~3 mm | 150-185 | Compact, good crush resistance | Standard shipping boxes, food, archiving |
| C-flute | ~4 mm | 120-145 | Versatile — the balance of everything | Shipping boxes, general packaging, e-commerce |
| E-flute (microflute) | ~1.5 mm | 290-320 | Thin, smooth surface — good for printing | Presentation packaging, displays, cosmetics |
| Double wall (BC or EB) | ~7 mm | — | Maximum strength — two superimposed waves | Heavy shipments (>15 kg), TV and picture boxes, international moves |
A fact few people know: C-flute is the most widely used in the world. You'll find it in most standard shipping boxes. But when you need real protection — moving, electronics, heavy objects — A-flute or double wall are what make the difference.
Single wall vs double wall: when it's worth paying more
The million-dollar question. The price difference between single wall and double wall is a few cents per box, but the difference in protection is brutal.
| Characteristic | Single wall | Double wall |
|---|---|---|
| Thickness | 3-5 mm (one wave) | 6-7 mm (two waves) |
| Maximum weight | 10-20 kg | Up to 30 kg |
| Stacking | 2-3 boxes on top | 5+ boxes on top |
| Price | More economical | 10-20% more expensive |
| Ideal for | Clothing, books, household items, light e-commerce shipments | Electronics, glassware, furniture, pallets, moves |
Practical rule: if the contents weigh less than 10 kg and are not fragile, single wall. If they weigh more than 10 kg, are fragile, or the boxes will be stacked on a pallet, double wall without hesitation. The few cents difference is infinitely cheaper than a return due to a broken product.
How is cardboard strength measured?
In the packaging industry, two main tests are used. You don't need to memorize the acronyms, but you do need to understand what they measure:
ECT (Edge Crush Test): How much pressure the cardboard can withstand when compressed on its edge. The higher the ECT, the more boxes you can stack without them crushing. This is the important data if you palletize or store boxes on top of each other.
BCT (Box Compression Test): How much weight the assembled box can withstand. It depends on the size of the box and the type of flute. It's the most practical test — it tells you directly if your box will hold up during storage and transport.
The ECT data usually appears on the technical sheet of the boxes. If you don't see it, as a reference: single-wall boxes usually have an ECT of 23 (standard) and double-wall boxes an ECT of 42-48.
What type of corrugated cardboard do you need?
Let's get practical. Depending on the weight of your product and how it will travel:
| Product weight | Recommended flute | Box type |
|---|---|---|
| Up to 5 kg | B or E-flute | Self-assembling boxes, small postal boxes |
| 5-15 kg | C or A-flute | Standard flap boxes, shipping boxes |
| 15-30 kg | A-flute or double wall | Reinforced boxes, moving boxes |
| More than 30 kg | Double wall mandatory | Industrial boxes + corner protectors + stretch film |
For shipments of fragile objects — regardless of weight — always go up one flute level. It's better to spend a few extra cents on the box than to pay for a return of a broken product. If you need a step-by-step guide to protecting delicate items, we have a specific article on how to pack fragile products.
Difference between corrugated cardboard and paperboard
Many people confuse them, but they are completely different. Corrugated cardboard has internal corrugations that give it structural strength. Paperboard is a flat, thin sheet, without waves — it's what you find in cereal boxes, perfumes, or medicines.
Paperboard is for presentation; corrugated cardboard is for protection and transport. If you want to delve deeper into the differences, we have a detailed comparison: paperboard vs corrugated cardboard. And for a complete overview of all existing types, consult our guide to packaging cardboard types.
Is corrugated cardboard sustainable?
Yes, and quite a lot. Corrugated cardboard is one of the packaging materials with the best environmental profile. It is mostly manufactured with recycled fiber (in Spain, more than 80% of packaging cardboard comes from recovered paper), it is 100% recyclable in the blue bin, and it biodegrades in a few weeks if it ends up in the environment.
The new European Packaging and Packaging Waste Regulation (PPWR) that will come into force in the coming years puts cardboard in a good position compared to plastics and composite materials. If you are interested in packaging sustainability, we have an article dedicated to eco-friendly packaging and sustainable alternatives.
Frequently asked questions about corrugated cardboard
What is corrugated cardboard and what is it used for?
Corrugated cardboard is a packaging material composed of layers of kraft paper with one or more internal wavy sheets. The corrugated structure gives it crush resistance, cushioning against impacts, and thermal insulation. It is the most widely used material in the world for manufacturing shipping, moving, and transport boxes. At TeleCajas, they have corrugated cardboard boxes in over 200 sizes, available for 24-hour delivery.
What is the difference between single wall and double wall?
Single wall has a single wavy sheet and can withstand up to 15-20 kg. Double wall has two superimposed wavy sheets and can support up to 30 kg. Double wall also resists stacking much better — you can place 5 or more boxes on top without them deforming. The price difference is a few cents per box, but the protection is significantly greater.
How much weight can a corrugated cardboard box hold?
It depends on the type of flute and the size of the box. As a reference: single wall (B or C) supports 10-20 kg, A-flute supports 15-25 kg, and double wall supports up to 30 kg. For loads over 30 kg, double wall with cardboard corner protectors is recommended to reinforce the structure.
Which cardboard flute is best for e-commerce?
For most e-commerce shipments, C-flute (single wall) is sufficient — it covers products up to 10-15 kg. If you ship fragile or heavy items, upgrade to double wall. Self-assembling single-wall boxes are the most popular in e-commerce due to their quick assembly and good finish. At TeleCajas, they have self-assembling boxes and postal shipping boxes in all standard sizes.
Is corrugated cardboard recyclable?
Yes, it is 100% recyclable in the blue bin. In Spain, more than 80% of packaging cardboard is made from recycled fiber. It is also biodegradable. It is one of the most sustainable packaging materials available.
Where to buy corrugated cardboard boxes in Spain?
