Corrugated shipping and export packaging
Board structure selected around stacking, transport and protection requirements — with ECT edge-crush testing and related calculations used as the basis for structural decisions, rather than grammage alone.
Why grammage is the wrong basis for specifying a box
“How many grams is the board” answers a material question, not a performance question. At the same grammage, flute type, medium recipe and liner material can produce very different compression performance. Ordering on grammage tends to end in one of two ways: specifying heavy for safety and pushing cost up, or looking adequate on paper and crushing in the stack.
The more useful approach is to establish what the packaging has to survive, then work back to a board structure. That usually means establishing: unit weight, stacking height, storage and transit duration, whether the route is sea freight (high humidity measurably reduces box compression strength), and whether the box is handled repeatedly.
How ECT, BCT and stacking height relate
ECT (Edge Crush Test) measures a board’s edgewise compression strength and is the core input for estimating the compression strength of a finished box (BCT). BCT, combined with a safety factor and storage conditions, gives the stacking height the box can carry.
The value of this chain is that it is measurable and traceable — once a structure is selected it can be validated by edge-crush testing rather than estimated from experience.
- ECT edge-crush strength: a material property of the board, obtained by measurement.
- BCT box compression: estimated from ECT, box perimeter and board thickness; reflects the top load a finished box can carry.
- Safety factor: has to cover real-world degradation from storage humidity, stacking duration and handling impact. Sea freight and long storage justify more conservative values.
Common flute types and where they fit
Flute type sets board thickness, cushioning and flat-crush performance. Different flutes suit different transport situations:
- Single-wall B flute: thinner with good printability. Suited to small, light products and retail outer cartons.
- Single-wall C flute: a balance of thickness and cushioning; the more general-purpose choice for shipping packaging.
- Single-wall E flute: thin with a flat surface; suits small-to-medium items as a carton replacement and for display outer boxes.
- Double-wall (BC flute and similar): a marked increase in thickness and compression strength, for heavy goods, high stacking and long sea journeys.
- Triple-wall: for heavy equipment and very long transit distances.
A structural optimization example
For an e-commerce fulfilment customer shipping appliance parts in a five-ply corrugated transit box, flute and medium recipe were re-specified at unchanged grammage, then validated by edge-crush testing before sign-off.
The result was stacking capacity increased from 5 to 8 layers, with total box cost down around 8%. The point of the example is that structural change on its own can improve performance without adding material — sometimes while using less.
What to send for a quotation
Useful inputs: product dimensions and unit weight, required stacking height, storage and transit duration, transport mode (sea, air or road), export destination and target market, any vulnerable areas on the product, and whether there is a current box design to compare against.
| Flute | Typical thickness and character | Suited to |
|---|---|---|
| Single-wall E flute | Thin, flat surface, good printability | Small-to-medium items, display outer boxes, carton replacement |
| Single-wall B flute | Thinner, good flat-crush resistance | Small, light products and retail outer cartons |
| Single-wall C flute | Balanced thickness and cushioning | General-purpose shipping packaging |
| Double-wall (BC) | Markedly greater thickness and compression | Heavy goods, high stacking, long sea freight |
| Triple-wall | Thickest, highest compression | Heavy equipment and very long transit |
Common questions
How do you determine the strength of a corrugated box?
Corrugated packaging is designed around protection, stacking and transport requirements rather than grammage alone. ECT edge-crush testing and related calculations can be used to validate the selected board structure.
What is wrong with specifying a box by grammage?
Grammage describes material input, not performance. At the same grammage, flute type, medium recipe and liner material produce significantly different compression behaviour. The result is either inflated cost or a box that looks adequate but collapses in the stack.
What matters for boxes going by sea freight?
High humidity in sea freight measurably reduces box compression strength, so the safety factor should be more conservative. Design should be checked against actual stacking height and storage duration rather than unit box strength alone.
Can box strength be improved without adding cost?
In many projects, yes. Re-specifying flute and medium recipe at unchanged grammage, validated by edge-crush testing, is a common route. How much it helps depends on the existing design and the actual handling conditions.
Samples first, orders second
Tell us what you are packing; we ship the matching paper, finish and structure samples — or call to discuss sampling.