How to make a corrugated cardboard box stronger?

Worried your box will collapse during shipping? The contents are valuable, but the box feels weak. You can easily make it stronger and ensure everything arrives aafely and securely.

To make a corrugated cardboard box stronger, you should reinforce the seams and corners with high-quality packing tape, add internal supports like cardboard inserts or dividers, and consider doubling up by placing one box inside another. Selecting the right box from the start is also key.

When I first started in the packaging business over 16 years ago, I saw many clients frustrated with damaged goods. They often blamed the shipping company, but sometimes, the problem was the box itself. It's a common issue, but luckily, it's one with many simple solutions. You don't need to be a packaging expert to significantly improve the durability of your boxes. Let's look at some practical methods you can use right away. Understanding these techniques can save you a lot of money and stress.

How do you strengthen a cardboard box?

Are your packed boxes bulging at the sides? You fear they won't survive the journey. Use simple taping and reinforcement tricks to give any standard box extra strength and stability.

You can strengthen a cardboard box by applying packing tape using the H-tape method¹, which secures all seams and edges. Also, add cardboard inserts to reinforce the walls and corners² from the inside. For heavy items, doubling the box provides maximum protection.

From my experience, the simplest tricks are often the most effective. Just changing how you tape a box can make a huge difference. Amateurs often just run one strip of tape down the middle seam. Professionals use what we call the "H-tape method¹." You tape the main center seam first. Then, you tape along the two shorter edge seams. When you look at the top or bottom, the tape forms the shape of the letter 'H'. This technique seals all the openings and adds significant structural support to the box's weakest points. For even more strength, especially with heavier contents, I recommend adding internal reinforcements. You can cut flat sheets of cardboard and place them against the inner walls. Creating simple corner braces from folded cardboard³ and placing them in each of the eight corners also prevents the box from being crushed. These small steps transform a standard box into a much safer container.

How to increase the strength of a corrugated box?

Are you designing packaging and need more strength? Your standard box design isn't meeting durability tests. You can increase its strength by choosing better materials and adjusting the design itself.

To increase a corrugated box's strength, choose a board with a higher Edge Crush Test (ECT) rating⁴g](https://gifts-pack.com/what-is-the-process-to-check-the-strength-of-a-carton-box/)[^5] or a heavier linerboard. Selecting the right flute profile⁵, such as C-flute for stacking⁶ or B-flute for puncture resistance⁷, is also critical for performance.

When a client like Peter, a product designer, comes to us, he's thinking beyond just tape. He wants to know how to build strength into the box from the very beginning. The key lies in the material specifications. The Edge Crush Test (ECT) is a number you'll see on the box certificate. It tells you how much force the box can withstand on its edges before crushing. A higher ECT means better stacking strength. Another factor is the flute profile⁵, which is the wavy layer of paper between the flat linerboards. Different flutes offer different benefits. Here's a quick guide my team and I often share with designers.

Choosing the right combination of ECT and flute profile⁵ is the most fundamental way to ensure a box has the strength it needs for its specific job.

What makes corrugated cardboard strong?

Ever wondered why a simple paper box is so tough? It looks like just a few layers of paper. The secret is in its unique structure, which cleverly creates strength from simple materials.

Corrugated cardboard is strong because of its three-layer structure: two flat linerboards sandwiching a wavy, arched layer called the flute⁸. This construction creates a series of connected arches, similar to an I-beam, that resists bending, pressure, and impact effectively.

I've always found the engineering behind corrugated board fascinating. It's a perfect example of how a smart design can create something where the whole is much stronger than the sum of its parts. Think of it like a bridge. The arches in the fluted paper distribute weight and pressure across the entire sheet. This is why you can stack heavy items on a corrugated box without it immediately collapsing.

Here’s a breakdown of its components:

• The Inside and Outside Linerboards: These are the two flat pieces of paper on the outside. They provide a smooth surface for printing and handling, but more importantly, they are in tension and compression when the board is bent, which gives it rigidity.
• The Fluted Medium: This is the wavy, zig-zag layer in the middle. The arches of the flute are what provide the cushioning against impacts and give the board its stacking strength. The empty space within the flutes also acts as an insulator.

This combination of layers creates a lightweight material that is surprisingly rigid and durable. It’s a simple but brilliant piece of engineering that we see every day.

How is corrugated card strengthened?

Need your packaging to withstand moisture or extreme weight? A standard box won't do the job. Manufacturers use special treatments and construction methods to build superior strength into the board itself.

Corrugated cardboard is strengthened during manufacturing by using multiple walls, like double-wall or triple-wall constructions⁹. It can also be treated with special coatings or waxes to make it water-resistant¹⁰, or made with heavier, more durable paper linerboards¹¹ for a higher ECT rating.

In my 16 years running Giftspack, I've seen a huge evolution in specialized corrugated boards. Sometimes, you need more than just a standard box. For clients shipping internationally or sending very heavy industrial parts, we look at strengthening the board at the manufacturing level. The most common way is by adding more layers. A standard box is single-wall. For more demanding jobs, we use double-wall or even triple-wall board. Each additional layer of flutes and linerboard dramatically increases the box's stacking strength and resistance to puncture. Another method is through treatments. We can apply a wax coating to boxes for shipping produce, which prevents them from getting weak from moisture. There are also grease-resistant coatings for food packaging¹². It's all about matching the right type of strengthened board to the specific challenge.

By choosing these advanced options, we give our clients packaging that can stand up to almost any shipping condition.

Conclusion

Strengthening a cardboard box involves both simple hands-on tricks and smart material choices. Reinforce weak points, add internal supports, and always select the right type of board for the job.