Home › Field notes › Export Carton Specification and ECT: Board Grade, Edge Crush, Cube and

Modular Bag Pro · 2026-10-11 · 2,484 words · 11 min read

An export carton specification fixes board construction, the edge crush value, the internal dimensions, the closure and the marking, and those five fields together decide whether a container arrives holding saleable goods. Cartons are ordered from 500 units per reference, packed inside a 35-50 day production window and checked at packing to AQL 2.5, quoted FOB Xiamen. The boundary is that any minimum board strength demanded by a carrier or a retailer is set by that carrier or retailer, so the number is confirmed with them rather than carried over from an earlier programme, and none of this is legal advice.

What an Export Carton Specification Has to Fix Before It Can Be Quoted

A carton is bought as a commodity and behaves as a structural component. Five fields decide how it performs: the board construction, the edge crush value, the internal dimensions, the closure, and the marking. A quote requested on any subset of those five is a quote for whatever board the supplier had on hand.

Board construction is the flute profile and the number of walls. A flute is the arched middle layer, and its profile sets the balance between cushioning and stacking: a tall flute cushions and resists compression through thickness, a short flute gives a flat printable surface and better crush resistance per millimetre. Single wall puts one fluted medium between two liners; double wall puts two media between three liners; triple wall goes further again and is reserved for heavy or long-transit shipments.

Dimensions are stated as internal, because internal dimensions are what the product has to fit. A specification written as external dimensions leaves the board thickness undetermined, and two suppliers quoting the same external size deliver cartons with different usable space. The sequence is product size, packing arrangement, internal carton size, then external size derived from the chosen board.

Marking is the fifth field and the one most often left vague. Shipping marks, carton numbering, destination, gross and net weight, and any handling symbol are all part of the print, and export documentation practice is described in general terms by the US Department of Commerce. Which marks are mandatory for a given destination is confirmed with your broker.

Bottom line: Issue the carton enquiry with internal dimensions, board construction, the edge crush value, the closure method and the full marking list on one sheet, because a quotation taken on external dimensions alone is not comparable between two suppliers.

Single Wall, Double Wall and Triple Wall Compared

Wall count is the first decision and it is driven by stack height and journey length, not by habit. A carton at the bottom of a stack in a container carries the mass of everything above it for the whole transit; a carton in a parcel network carries almost nothing but has to survive impacts. Those two jobs want different board.

Double wall costs more per carton and saves more than it costs whenever the alternative is crushed bottom cartons. The arithmetic is simple: the board premium applies to every carton, while damage applies to the fraction that fails, and that fraction rises steeply once the stack exceeds what the board can carry. Programmes shipping by sea across 25-35 days routinely justify double wall on that arithmetic alone.

Thickness has a second cost that is easy to miss. A thicker board reduces the internal volume available inside a fixed external size, which means either a larger carton or fewer units per carton, and both change the container count. Cube is planned against 20GP ≈28 CBM and 40HQ ≈68 CBM, so a millimetre of extra board is paid for twice: once in board cost and once in lost cube.

Spec rule: Choose the wall count from the stack height the bottom carton will actually carry for the whole transit, then re-derive the internal and external dimensions from that board, because the cube lost to a thicker wall is paid again in container count.

Reading an Edge Crush Value: What It Predicts and What It Misses

The edge crush test compresses a short strip of board on its edge and reports the force per unit length at which it fails. It is a property of the board, not of the carton, and it is the number most buyers use to compare quotations because it is cheap to measure and easy to write down.

What it predicts is stacking performance: board with a higher edge crush value resists the vertical compression a stack applies. That makes it the right number when the dominant risk is a container stack standing for weeks. What it misses is everything else. It says nothing about puncture from a corner, nothing about performance after the board has absorbed moisture, and nothing about how the carton behaves when dropped.

Moisture is the gap that hurts most in sea freight. Corrugated board is hygroscopic: it takes up water from humid air and loses a large part of its compressive strength as it does. A container closed in a humid port and opened in a temperate one is exactly the environment where a board that measured well at the mill under-performs in service. Ventilation, container condition and storage at the destination all sit inside that risk.

The practical control is to specify the edge crush value at a stated conditioning, to require a certificate against the delivered lot, and to treat the value as one input among several rather than as the whole specification. Where the journey includes a parcel leg, the carton is qualified by a transit sequence rather than by board strength alone.

Verdict: Use the edge crush value to compare board quotations and to size a container stack, but never as the sole acceptance criterion, because it does not describe puncture behaviour, drop performance or the strength the board keeps after weeks in a humid container.

Carton Size, Pallet Pattern and Container Cube

Carton size is derived, not chosen. The product and its packing arrangement set the internal dimensions; the pallet pattern constrains the footprint; the container constrains the total. Working backwards from a preferred carton size produces a shipment that wastes cube and leaves cartons overhanging pallets.

The pallet pattern comes first among the constraints. A footprint that tiles a pallet with neither overhang nor a large void protects the cartons, because overhanging board is unsupported board and unsupported board is what gets struck by a forklift. Where two carton sizes serve the programme, they are chosen to combine into one pattern rather than each fitting a pallet only on its own.

Container cube then sets the count. Planning against 20GP ≈28 CBM and 40HQ ≈68 CBM is standard, and the realistic fill is below the nominal figure because cartons do not tile a container perfectly and because dunnage, pallets and loading sequence all consume space. A specification is quoted on the achievable count, not on the arithmetic maximum.

The order matters because a change at any checkpoint re-runs every decision below it. Changing the bag gauge changes the packed unit, which changes the internal carton, which changes the pallet pattern, which changes the container count — which is why the bag decision belongs in the polybag specification before the carton is drawn.

Selection rule: Derive carton size in the order packed unit, arrangement, internal dimensions, board, external dimensions, pallet pattern, container count, and never fix an external size first, because an externally fixed carton silently defines the board and the usable space.

Bursting Strength and Edge Crush Compared: Two Tests, Two Answers

Two board tests appear in carton specifications and they are not substitutes. Edge crush measures resistance to compression along the board edge; bursting strength measures resistance to a force applied through the face of the board. Both are properties of the board rather than of the finished carton, and each governs a different decision.

Which test governs depends on the journey. A container stack standing for weeks is governed by compression, so edge crush and a packed-box compression check are the relevant evidence. A parcel journey is governed by impacts, so a sequence test is the relevant evidence and board strength alone is not.

Sequence testing for individual packaged products moving through a parcel network is referenced as ISTA 3A, and it combines drop, vibration and compression in one run. Because the sequence is run on the packed unit, it exposes the interaction between product, bag and carton that a board certificate cannot.

Takeaway: Ask for the edge crush certificate when the risk is a standing stack and for a transit sequence report when the risk is handling, and treat a board certificate submitted against a parcel journey as evidence of the wrong thing.

Closure, Tape and Strapping: Where Cartons Actually Open

Cartons fail at the closure far more often than they fail in the panel. The board is usually adequate; the seam is what lets go, and it lets go for a process reason rather than a material one — wrong tape width, a dirty surface, insufficient dwell, or a glue pattern that never covered the flap.

Two closure decisions are worth stating explicitly. The first is tape width and overlap: a narrow tape on a heavy carton concentrates the load, and a short overlap leaves the centre seam unsupported. The second is the seal against dust — corrugated board carries surface dust from cutting, and pressure-sensitive tape applied over it grips the dust rather than the board.

Strapping is added where a carton is heavy enough to bulge. It prevents the bulge, but a strap tensioned too hard crushes the corner it is meant to protect, so corner protectors are specified together with the strap rather than after it.

Judgement: Specify closure as tape type, tape width, overlap length and surface preparation rather than as "sealed", and add strapping with corner protection for heavy cartons, because the seam is where a carton opens long before the panel fails.

How Under-Specified Cartons Fail: Damage Patterns by Journey Stage

Damage has a signature, and reading it tells you which field was under-specified. A crushed bottom carton in a container is a stack problem. A burst seam is a closure problem. Panel puncture at a corner is a board problem. Crushing that appears only on the outer cartons of a pallet is a pallet-pattern problem, not a board problem.

The journey stages each add their own load. Warehouse stacking applies sustained compression. Container loading adds point loads from equipment. Sea transit adds a long, humid dwell with vessel motion. Destuffing adds impacts from handling equipment and from cartons being dragged rather than lifted. A carton specified for the first stage only will fail at the third.

Under-specification is usually a purchasing decision made months earlier. Where a programme has run for several seasons without damage reports, the temptation is to step the board down to recover margin. That works until the routing changes, the dwell lengthens, or the destination warehouse changes its handling equipment, and then the same board that was adequate for years starts generating claims.

The defensible approach is to specify the board against the worst routing the programme actually uses, to record that routing with the specification, and to re-qualify when the routing changes. Inspection at packing to AQL 2.5 catches carton defects that are visible, but it cannot catch a board that is adequate in the laboratory and marginal in a container.

Programme Facts: How Carton Packing Is Run and Checked

Our production team runs carton packing to a written packing specification that names board, dimensions, closure and marking, and any change to that specification is treated as a change to the product rather than as a bench decision. Carton markings are checked against the shipping documents before the container is loaded.

Vetted partner facilities provide 4,950 m² of SGS-verified floor, 137 people, 7 production lines and 149 machines, and monthly capacity near 200,000 units. Experience in bag production goes back to 2004 for the founder, and the business was set up in 2014, so packing specifications are written by people who have watched cartons come back damaged.

Carton Cost, Freight and the Price of One Extra Millimetre

Carton cost is a board-cost line and a freight line at the same time. Board is bought by area, so a larger carton costs more per unit; freight is bought by cube or by container, so a larger carton also costs more to move. The two effects compound, and neither appears on the carton invoice.

The freight effect is the larger of the two on a sea shipment. Filling 20GP ≈28 CBM or 40HQ ≈68 CBM with slightly larger cartons can drop the unit count enough to force an extra container, and one extra container outweighs a season of board savings. Transit sits at 25-35 days by sea, 5-8 days by air and 3-5 days by express courier, and only the sea leg makes cube the dominant cost.

Damage is the third line and the one that gets forgotten until it happens. A damaged carton costs the article, the re-pack labour at the destination, and the claim handling time. Because damage is probabilistic and board cost is certain, the board decision is made on expected damage, which is why the worst routing in the programme sets the specification rather than the average one.