June 8 2026
When you're shopping for custom boxes, the term "corrugated" comes up constantly. But what does it actually mean, and more importantly, why should you care whether you get single wall or double wall?
Here's the thing: the difference between these isn't just technical jargon. It's the difference between a box that holds up beautifully through delivery and one that arrives at your customer's door looking like it's been through a rugby match.
The good news is that this isn't complicated science. You don't need a degree in packaging engineering to make the right choice for your products. You just need to understand a few practical principles about how corrugated boxes work, what the numbers mean, and what your actual products demand.
In this guide, we'll break down the structure of corrugated cardboard, explain the different flute types and what they're designed to do, and walk through the decision process for choosing between single and double wall options. By the end, you'll understand not just what to order, but why you're ordering it.
Corrugated cardboard isn’t a solid sheet. It’s a sandwich: two flat layers (called liners) with a wavy, rippled middle layer (called fluting) between them. That ripple is where the magic happens.
The ripple creates strength while keeping weight low. It’s the same principle that makes corrugated metal roofing so strong despite being thin. The waves add structural support without adding material cost. A single wall of corrugated cardboard might only be 3-4mm thick, but it’s dramatically stronger than a flat sheet of the same thickness would be.
This design is why corrugated cardboard has become the default for shipping and storage. It protects contents brilliantly while remaining economical enough that you’re not paying a fortune for packaging.
The wave size matters. Different “flute types” (which refers to the size and spacing of the ripples) offer different benefits, and selecting the right one changes both how much protection you get and how much you’ll spend.
A flute corrugated boxes have the largest ripples, roughly 5mm tall. This is your most economical option. Because the waves are bigger and farther apart, you use less material.
A flute is ideal for lightweight items where impact protection isn’t the primary concern. Think packaging for clothing, books, or other light goods. The cushioning is minimal, but the cost is lower than other options.
Downside? If your product is fragile or heavy, A flute on its own might not provide enough protection. The larger gaps between waves mean less overall strength to compress and distribute stress.
B flute sits in the middle: roughly 3.5mm waves. It offers a solid balance between economy and protection.
This is the workhorse of corrugated packaging. For most small e-commerce businesses, B flute single wall is sufficient. The medium wave size gives you decent protection without the cost premium of finer fluting.
B flute is commonly available in single wall options at reasonable cost, and upgrading to double wall B flute doesn’t represent a massive price jump if you need extra strength.
C flute has the smallest, tightly spaced ripples, roughly 2.3mm tall. This design gives superior stacking strength and better protection than A or B flute.
C flute costs more than A or B, but the protection improvement is real. If you’re stacking boxes in a warehouse, shipping heavier items, or concerned about rough handling, C flute is worth the investment.
E flute (1.5mm, extremely fine) is used for premium presentation packaging and cases where you need excellent printing quality. It’s not typically used for shipping protection because the fine waves don’t cushion effectively.
F flute and N flute exist as specialty options in some markets, but you’ll rarely encounter them for standard custom shipping boxes.
You’ll see “Mullen burst strength” or “ECT (Edge Crush Test)” numbers on technical specs. These tell you how much pressure a box can withstand before it fails.
ECT is measured in pounds per inch. A box with 23 ECT can handle 23 pounds of crushing force per linear inch before the top or bottom fails. 32 ECT is stronger. 44 ECT is industrial-strength.
For most small businesses shipping products under 5kg, 23 ECT single wall corrugated is perfectly adequate. If you’re shipping heavier items, stacking boxes, or exposing them to rough warehouse handling, moving to 32 ECT (or double wall) makes sense.
Real example: A bookshop shipping boxes of mixed books, averaging 3kg per box, finds 23 ECT single wall performs well. They stack boxes four-high in the warehouse, and the weight of three boxes below doesn’t crush the bottom box. Same specifications, but if they move to 6kg boxes, suddenly the weight concentration at the bottom creates problems. That’s when double wall or upgraded single wall becomes necessary.
Single wall corrugated has two layers of cardboard liner (top and bottom) with a single layer of fluting between them. It’s lighter, cheaper, and adequate for most purposes.
Double wall has two layers of fluting, separated by another middle liner, creating two rippled sections. Total thickness is roughly double. The protection is substantially better.
A single wall custom corrugated box, 300x200x150mm in B flute, might cost 35-50p per unit at modest quantities (500-1000 boxes). The same box in double wall costs 60-85p per unit.
That’s a significant difference. If you’re ordering 1,000 boxes monthly, you’re looking at £350-500 for single wall versus £600-850 for double wall. For many small businesses, that difference matters to margin.
Single wall corrugated works brilliantly if your products are:
Lightweight (under 2kg per box). The box itself carries most of its own weight, and light items don’t place stress on the structure.
Not fragile (or well-protected internally). If your product survives a reasonable drop or impact without damage, the external protection matters less.
Not stacked. If boxes are shipped individually and don’t sit under weight in a warehouse, you don’t need the crushing strength double wall provides.
Destined for careful handlers. If your customer is receiving the package immediately (not a warehouse sitting on it for weeks), single wall is less likely to experience progressive degradation.
Double wall corrugated justifies the cost when:
Your products are fragile (ceramics, glass, electronics). The extra cushioning layer significantly reduces the shock transmitted to contents during impact.
You’re shipping weight (over 5kg per box). Heavy products concentrated in one box place real stress on the structure. Double wall handles this without collapsing.
Boxes are stacked in warehouses. If your boxes sit three or four high in storage, the crushing force on the bottom box is genuine. Double wall prevents that structural failure.
Your boxes might experience rough handling. Warehouse equipment, courier loading, customer roughness – these are real forces. Double wall is your insurance policy.
Your brand requires premium presentation. Double wall boxes are noticeably more robust when they arrive, which sends a quality signal to customers.
Real scenario: A craft brewery ships six bottles per box (roughly 4kg). In single wall, the accumulated weight of stacking is causing the bottom boxes’ bottoms to bow slightly. They test with double wall, and the problem vanishes. The cost increase (approximately 40p per box on 500-unit orders) is easily recovered through fewer damaged products and customer complaints.
The decision matrix is simpler than you’d think.
Lightweight, non-fragile items: Single wall B flute. Cost-effective, perfectly adequate. This works for clothing, books, non-perishable food items.
Lightweight items with moderate fragility: Single wall C flute or double wall B flute. Choose based on budget and handling expectations. If you expect rough treatment, double wall B is better than single wall C.
Moderate weight (2-5kg), moderate fragility: Double wall B flute. This is your sweet spot for most e-commerce. Protection is solid, cost is reasonable, and it performs well in real-world scenarios.
Heavy items (5kg+) or very fragile: Double wall C flute. Maximum protection. Cost is higher, but so is the value of products that arrive undamaged.
The flute type you choose affects how your box prints. A flute is grainier; finer flutes (C and E) print crisper, sharper graphics. If your branding is critical, factor this into your decision.
Double wall boxes offer a premium feel that customers notice. The weight, the sturdiness – these communicate quality before the box is even opened. For premium products, this perception is worth the cost investment.
The challenge many small businesses face is that suppliers demand minimum orders of 2,000 or 5,000 boxes, even when you only need 500 to test. This forces you to commit capital to inventory before you know if the specification is right.
Specialists like Boxtopia solve this by offering no minimum orders. You can order 100 custom corrugated boxes in double wall C flute if that’s what you need. Your per-unit cost is naturally higher than someone ordering 10,000, but you’re not forced to commit to massive inventory before validating your choice.
This is genuinely valuable for testing. Order 200 boxes of a new specification, use them in your actual operation for a month, then decide whether to scale up or adjust the specification.
Corrugated boxes aren’t one-size-fits-all, and understanding the difference between flute types and wall structures lets you make smart choices rather than default ones. Single wall B flute is economical and works for most lightweight items. Double wall adds meaningful protection for heavier products and rough handling scenarios, and the cost increase is justified if it prevents damaged shipments and unhappy customers.
Start by assessing what your products actually demand: weight, fragility, stacking scenarios, and handling expectations. Match that against the options. Test before you commit to larger quantities. And work with suppliers who understand that small businesses need flexibility.
The right box specification isn’t about maximising protection or minimising cost; it’s about finding the balance that protects your products and your margins simultaneously. That’s what good packaging does.
