How to increase the strength of a corrugated box?

Your products are getting damaged during shipping because the boxes are weak. This leads to costly returns and unhappy customers, hurting your brand's image. Let's fix this problem for good.

To increase the strength of a corrugated box, you must focus on three key areas: selecting the right materials (paper weight and flute type), optimizing the structural design of the box, and ensuring high-quality manufacturing processes like proper gluing and scoring.

A strong box is more than just thick paper. It's a combination of different strengths working together. You have to consider bursting strength¹, which stops punctures, and compression strength², which allows stacking. For someone like me, who has been in this industry for over 16 years, I've learned that understanding these different aspects is the key to creating packaging that truly protects a product. It’s not about just picking the strongest option, but the right option for the specific job. Let’s break down how you can improve each type of strength to build a better, more reliable box.

How to increase the bursting strength¹ of a corrugated box?

Are your boxes ripping open from pressure inside? This is a common failure that exposes your products to damage and makes your packaging look cheap and unreliable to the end customer.

To boost bursting strength¹, you must use a higher-grade linerboard with a greater basis weight. This paper, measured by the Mullen Burst Test³, has stronger, often virgin, fibers that better resist puncture and tearing forces from both inside and outside the box.

Bursting strength is all about the quality of the linerboards, which are the flat paper surfaces on the inside and outside of the corrugated sheet. The Mullen Test tells us how much force the paper can take before it ruptures. The primary way to improve this is by increasing the basis weight of the linerboard⁴, which simply means using a heavier, denser paper. In my experience, the type of paper is just as important. For a client shipping heavy metal parts with sharp corners, we saw constant failures. Their boxes were bursting. The solution was simple but effective: we switched their standard "Test" liner to a heavier "Kraft" liner. Kraft liner⁵ is made from virgin wood pulp, which has longer, stronger fibers than the recycled fibers in Test liner⁶. This small change completely solved the bursting problem, securing their product and saving them from costly damages.

Here's a simple breakdown of how linerboard choice affects bursting strength¹:

How to make cardboard boxes stronger for stacking?

Are your boxes getting crushed in the warehouse or during transport? This is a serious issue that leads to product loss and can make your entire supply chain inefficient and unsafe.

To make cardboard boxes stronger for stacking, you need to improve their compression strength². This is achieved by selecting a suitable flute profile, like a C-flute⁷ or double-wall BC-flute⁸e](https://leader-display.com/what-are-the-different-types-of-cardboard-displays-for-retail/)[^7], and using a high-quality corrugating medium between the linerboards.

When we talk about stacking strength, we're really talking about the results of two key tests: the Edge Crush Test (ECT)⁹ and the Box Compression Test (BCT)¹⁰. The ECT measures how much force the edge of the board can take before crushing, which directly relates to the final box's stacking ability. This strength comes mainly from the flutes—the wavy paper inside the walls. A thicker, more robust flute like a C-flute⁷ or a double-wall combination (like BC-flute⁷) provides much more vertical support. I worked with a beverage company whose single-wall boxes were sagging on the pallets. We redesigned their packaging using a double-wall board. The extra layer of fluting increased their BCT value so much that they could safely add another full layer of products to each pallet. This not only stopped the damage but also saved them thousands in warehouse space and shipping fees.

Choosing the right flute is crucial for stacking performance:

How can structural design increase box strength?

You've chosen good materials, but your boxes are still failing. A poor structural design can weaken even the best corrugated board, leading to unexpected collapses and product damage.

To increase box strength through design, create dimensions that are as close to a cube as possible. This shape distributes weight more evenly. Additionally, adding internal structures like inserts and partitions¹¹ will dramatically increase compression strength² and overall rigidity.

A box's strength isn't just in its walls; it's in its overall design. First, the shape matters. A tall, narrow box is much more likely to tip and buckle than a box that's closer to being a cube. The cube is the strongest shape because it distributes forces evenly across all its panels. Second, and this is a trick I use all the time, internal components are a game-changer. For a client shipping fragile glass bottles, the outer box material was already quite strong. Instead of making it even thicker and more expensive, we designed a simple corrugated divider. This insert created individual cells for each bottle, preventing them from clanking together. More importantly, the dividers acted as internal support columns, massively increasing the box's stacking strength. This small addition solved both the protection and the stacking issue in one go, and the cost was much lower than upgrading to a heavy-duty double-wall box.

Always remember: the flutes must be oriented vertically for stacking strength. If they run horizontally, the box will have almost no ability to support weight.

What makes corrugated cardboard so strong?

Have you ever stopped to think about how a few layers of paper create such a strong and durable structure? Understanding this simple engineering principle is key to designing better packaging.

The strength of corrugated cardboard comes from its three-part sandwich structure¹². Two flat linerboards hold a wavy, arched layer of paper called the flute. This design acts like an I-beam, creating a lightweight material with exceptional rigidity and resistance to bending forces.

The secret to corrugated board is its inner architecture. It's a perfect example of engineering where the whole is much stronger than the sum of its parts. Think of it like a series of connected arches, one of the strongest architectural shapes.

Let's break down the role of each component:

• The Linerboards: These are the two flat sheets on the outside. They provide the board's tensile strength and bursting strength¹. They also provide the smooth surface needed for printing.
• The Medium (Flute): This is the wavy paper in the middle. The arches of the flute¹³ provide cushioning against impacts. When stood on their edge, these arches act like columns that give the board its compression strength² for stacking.
• The Adhesive: The starch-based glue¹⁴ that holds these three layers together is the unsung hero. If the adhesive bond is weak, the layers can separate (called delamination¹⁵), and the board loses almost all its structural integrity.

This I-beam structure is incredibly efficient. It provides maximum strength with minimum material, which is why it has been the go-to choice for shipping for over a century. However, remember that humidity is its biggest enemy. Moisture weakens the paper fibers and the glue, causing the arches to sag and the box to lose its strength.

Conclusion

To make a stronger box, you must balance material choice, structural design, and internal supports. It's about using the right combination to protect your product effectively and efficiently.