Single Wall vs Double Wall Letterbox Boxes: Which Is Stronger?
Single vs double wall for letterbox boxes: strength, practicality, and the thickness trade-off.
Can letterbox boxes be double wall?
Double-wall construction is technically possible for letterbox boxes but rarely practical. Double-wall board is typically 5-7mm thick per wall, which would consume most of the 25mm total thickness limit, leaving very little space for the actual product.
Quick answer
Single wall is the standard and most practical choice for letterbox boxes. The 25mm thickness limit makes double wall impractical for most products. E-flute (1.5mm) single wall provides adequate protection for typical letterbox items while maximising internal space. B-flute (3mm) offers more protection but reduces product space. Double wall should only be considered for very high-value, very thin items.
Practical considerations
At 1.5mm per wall (3mm total), E-flute leaves maximum space for products.
The loads are minimal, so heavy-duty construction is rarely needed.
For letterbox items, the risk is bending, not crushing. Even E-flute provides adequate rigidity.
Board choices: materials guide or engineering guide.
When single wall is sufficient
For virtually all letterbox applications, single-wall E-flute or solid card is sufficient. The items being shipped are thin and light by definition. The main protection needed is against bending during transit, which single-wall corrugated board handles effectively.
Single wall letterbox boxes
E-flute letterbox boxes that maximise product space within Royal Mail limits.
Browse letterbox boxesFrequently asked questions
Single wall for almost all applications. Double wall is impractical within the 25mm thickness limit.
1.5mm thick corrugated board. The standard for letterbox boxes, providing protection while maximising product space.
Yes, for the light items that fit in letterbox boxes, E-flute provides adequate rigidity and bend resistance.
Only for extremely high-value, very thin items needing maximum protection, and only if thickness allows.
Micro-flute (0.8mm) or heavy solid card for ultra-thin letterbox boxes.
Part of our guide
Product Guide: Letterbox Boxes
Expert guides on letterbox packaging, from sizing and Royal Mail rules to branding and sustainability.
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