A packing specification for ocean-shipped glass should fix four things in writing before mass production: 5-ply corrugated cartons with a stated edge crush test (ECT) value, dividers cut to the bottle's maximum diameter plus 3 to 5 mm, column-stacked pallets with no carton overhang, and a container loading plan. Most transit breakage traces back to one of these being left vague, not to the glass. A bottle can pass a 1.2-meter drop test and still arrive crushed after 30 days at sea if the board is too weak or the pallet pattern lets cartons hang over the deck.
What the packing specification sheet must state
The sheet is issued before production starts and the order ships against it. If packing details first appear when the container is opened, there is nothing to hold a claim against. Ask for these fields:
- Carton ply count and ECT rating
- Divider material and cell dimension
- Pieces per carton and cartons per pallet
- Pallet size and ISPM-15 status
- Layer pads and corner boards
- Number of shrink-wrap revolutions
- Container loading plan with the pallet count
- Target breakage allowance and the remedy if it is exceeded
A supplier who cannot produce this document is usually handing the packing to a third-party warehouse, which leaves your breakage risk undefined. "Export packing" that amounts to a thicker box is not a specification. Our RFQ checklist for bottles and jars shows how to ask for these fields in a first inquiry, and the page on export support for glass bottle orders explains where packing sits alongside freight and documents.
Cartons: board grade and how bottles sit inside
The carton's task is to hold each bottle so that a knock is absorbed by the board and never passes from glass to glass. Board grade, divider and fill arrangement have to be chosen as one system.
Board grade
The 3-ply cartons common in Chinese domestic distribution are not suitable for export. The minimum we specify is 5-ply BC-flute corrugated board with burst strength of 200 psi or more and an ECT of at least 44 lb/in where pallets will be double-stacked. Heavy spirits bottles above 500 g each move up to 5-ply EB-flute at ECT 51.
Write the ECT value into the purchase clause and require the carton certificate with each shipment. A ply count on its own cannot be enforced, because two 5-ply boards can differ widely in compression strength.
Fill arrangement
Bottles go in neck-up, so the base, the heaviest part, rests on the carton floor. Where a carton holds two layers, an H-board or corrugated pad separates them. A top pad takes up the space above the neck finish; without it, the weight of a second pallet can press closures into the lid.
Corrugated or molded pulp dividers
Dividers do two jobs: they keep bottles apart and they carry part of the vertical load. The choice between the two materials follows the bottle shape and the length of the voyage.
| Divider | Suits | Why |
|---|---|---|
| Corrugated | Cylindrical and lightly shouldered bottles: wine, juice, most jars | The default choice; quick to tool and recycled together with the carton |
| Molded pulp | Heavy-shouldered spirits bottles, long sea routes | Cradles the shoulder radius and stands up to vibration abrasion that can wear through corrugated walls over 30-plus days in a container |
Either way, the cell is sized to the widest point of the bottle with 3 to 5 mm of clearance. Less than that and decoration scuffs during high-speed packing; more and the bottle moves sideways in transit.
Pallet patterns built around the container
Many of the pallet failures that end in claims come from a pattern laid out for warehouse handling instead of container dimensions. An ISO dry container is 2,352 mm wide inside, and a 40HQ is 2,690 mm high inside. Two pallets have to sit side by side with clearance, which is why export glass nearly always travels on 1,100×1,100 mm or 1,200×1,000 mm pallets.
Overhang does the most damage. Corrugated board carries load down through its walls, so a carton edge that projects past the pallet deck has nothing beneath it. A 20 mm overhang cuts effective board strength by roughly 30 percent, and as the container flexes at sea the stress concentrates on that unsupported edge. Collapsed bottom layers are the typical result.
For glass we specify:
- Column stacking, not an interlocking brick pattern. Brick patterns are steadier in transport but give up vertical compression strength.
- A layer pad every second layer
- Corner boards on all four vertical edges
- A top sheet to keep condensation drip off the cartons
- At least three shrink-wrap revolutions at the pallet base
Wooden pallets must be heat-treated and marked to ISPM-15 for almost every destination. Molded presswood pallets are increasingly chosen, particularly for the EU: they are exempt from ISPM-15, their dimensions are consistent enough for automated unloading, and there is no HT mark to go missing and delay customs clearance.
How many bottles a 40HQ holds
Two limits apply, and the lower one wins. A 40HQ has about 76 m³ of internal volume, and on most trade lanes the practical payload stops near 26 tonnes. Light, bulky formats such as small jars and 300 g wine bottles fill the space first. Heavy ones, such as 550 g spirits bottles or heavy-base perfume flacons, come close to or reach the weight limit first. Work out the piece count under each limit, take the smaller, and then check it against a loading plan drawing.
| Loading parameter | 750ml wine bottle (~300 g) | 500ml spirits bottle (~550 g) | 212ml food jar (~160 g) |
|---|---|---|---|
| Pieces per carton | 12 | 12 | 24 |
| Carton dimensions | ~400×300×330 mm | ~400×300×290 mm | ~400×270×200 mm |
| Gross carton weight | ~5.5 kg | ~8.4 kg | ~5.6 kg |
| Pallet size | 1100×1100 mm | 1100×1100 mm | 1200×1000 mm |
| Cartons per pallet | 100 | 80 | 120 |
| Pallets per 40HQ | 44 | 40 | 40 |
| Pieces at the volume limit | 52,800 | 38,400 | 115,200 |
| Pieces at the 26 t weight limit | ~72,000 | ~40,900 | ~140,000 |
| Limit that binds | Volume | Volume, with payload close behind | Volume |
| Planned load with safety margin | ~50,000 pcs | ~37,000 pcs | ~110,000 pcs |
These are representative figures for planning only. The real numbers come from the project drawing, the final packing specification sheet and the carrier's payload rules on your lane. Freight cost per piece is likewise worked out per lane.
When a new bottle shape needs new packing validation
A stock-mold bottle already has a carton and divider set that has been proven on that shape, so validation is a matter of re-issuing the existing specification sheet. That suits a first import or a market test.
Modified-stock and custom-mold projects change the bottle geometry, and the old divider set no longer fits. New divider tooling and a fresh drop test then become required items in the project, on top of the mold work itself. Include them when you compare sourcing routes; packing is one of the first places an unusually low quotation saves money, and the saving comes back as breakage on arrival.
For any new bottle or divider design, we ask for pre-production packed samples to be tested to an ISTA 3A-aligned protocol: drops from 1.2 meters, random vibration that simulates ocean transit, and compression on the full pallet. The report is attached to the packing specification as an annex, so the sheet records tested performance. Our page on pre-shipment quality inspection describes how packing is verified again at final QC.
What to send for a packing specification
When you request a quote, these details let us draft the packing specification alongside it:
- Bottle drawing or dimensions: height, maximum diameter, shoulder profile and weight
- Preferred pieces per carton, and any retail-ready packaging requirement
- Destination port, warehouse racking, and whether pallets will be double-stacked on arrival
- Pallet type: heat-treated wood to ISPM-15, or presswood
- The breakage allowance and claim remedy you want in the contract
Frequently asked questions
What carton clause should go into a purchase contract for sea freight?
Name 5-ply corrugated board and tie it to a test rating: ECT 44 as the baseline, ECT 51 for bottles over 500 g. Add the divider type and the 3 to 5 mm cell clearance, and make the carton certificate a required document.
How many glass bottles fit in a 40HQ?
As planning figures, around 50,000 wine bottles of 750ml at 300 g, about 37,000 spirits bottles of 500ml at 550 g, or more than 100,000 small food jars. The exact count depends on carton size, pallet pattern and the payload allowed on your lane.
Do glass bottle imports need fumigated wooden pallets?
Wooden pallets need heat treatment and the ISPM-15 mark for virtually all destinations. Presswood pallets fall outside that rule, which is why many importers now specify them.
Can the packing be tested before mass production?
Yes, and it should be whenever the bottle or the divider is new. Drop, vibration and full-pallet compression tests on packed pre-production samples show whether the specification works before the order is committed to it.