Choosing a cardboard box sounds simple until you're stood in the stockroom wondering whether the one in your hand will survive a courier's journey. Get it wrong and you either pay for over-engineered packaging you don't need, or you risk damaged goods and unhappy customers. The good news is that box strength isn't a mystery once you understand a few basics. Here's a straightforward guide to single wall versus double wall corrugated board, and how to match the right box to the job.
How corrugated cardboard is actually made
Corrugated board isn't just thick paper. It's a sandwich of flat outer sheets (called liners) with a wavy, fluted layer glued in between. Those flutes are the clever bit: the arches give the board its rigidity and cushioning, much like the arches in a bridge. The more layers of fluting you add, the stronger and more protective the board becomes.
You'll come across a few common terms:
- Single wall — one layer of fluting between two liners. This is the everyday box most people picture.
- Double wall — two layers of fluting and three liners, making a noticeably stiffer, tougher board.
- Flute grade — letters such as B, C, E and BC that describe the size of the flutes. Smaller flutes (like E) give a smooth surface and good print; larger flutes give more cushioning.
Single wall boxes: the reliable all-rounder
Single wall cardboard is the workhorse of everyday packing. It's light, cost-effective, easy to store flat and perfectly capable for the majority of parcels. If you're sending clothing, books, small homeware, most retail products or lightweight food packaging, single wall will usually do the job without fuss.
Single wall boxes typically suit contents up to around 10–15kg, depending on the exact grade and box size. They're also kinder to your storage space and your postage costs, since they weigh less than heavier board.
Good jobs for single wall
- Retail orders and general e-commerce parcels
- Lightweight, non-fragile items
- Short courier journeys with gentle handling
- Anything where you want to keep weight and cost down
Double wall boxes: for weight, protection and rough journeys
Double wall board comes into its own when things get heavier, more fragile, or when a parcel is going to be handled a lot. The extra layer of fluting resists crushing far better, holds its shape under a stack, and gives more protection against knocks and drops.
If you're shipping ceramics, glassware, bottles, electricals, machinery parts or anything valuable, double wall is a sensible upgrade. It's also the better choice for boxes that will be stacked on a pallet, where the weight of everything above bears down on the walls below.
Good jobs for double wall
- Heavier items, roughly 15kg and above
- Fragile or high-value goods
- Long-distance or multi-leg deliveries
- Boxes destined for pallet stacking or long-term storage
How to choose the right strength
Rather than always reaching for the strongest option, think about three things: the weight of the contents, how fragile they are, and the journey ahead. A heavy but sturdy item on a short trip may be fine in single wall, while a light but delicate item on a long journey might justify double wall for peace of mind.
A few practical pointers:
- Match the box to the contents, not the other way round. Buying a box that fits properly matters as much as the board grade. A well-fitted single wall box often outperforms an oversized double wall one full of loose gaps.
- Fill the voids. Even the toughest board can't protect contents that rattle around. Use paper, bubble wrap or inserts to stop movement.
- Don't over-pack. Cramming a single wall box beyond its comfortable weight is a false economy.
- Test before you commit. Pack a sample, seal it well and give it a gentle shake and a controlled drop. It tells you more than any spec sheet.
Sizing is just as important as strength. If your boxes are too big, you'll waste money on void fill and volumetric postage; too small and you'll strain the seams. Our guide on how to measure cardboard boxes for shipping walks through getting the dimensions right the first time.
Getting your wider packaging in order
Box strength is one piece of a bigger picture. As your orders grow, it pays to review everything from tape and void fill to labels and returns packaging so it all works together. If you're building or refining your setup, our simple packaging checklist for growing businesses is a handy starting point.
In short: reach for single wall for everyday, lighter parcels, and step up to double wall when weight, fragility or a rough journey demands it. Choose the right size, fill the gaps, and you'll protect your products while keeping costs sensible.