Wall thickness is one of those specifications that buyers rarely ask about and then pay for. It determines whether your order arrives intact or whether you are writing off a percentage of stock before it reaches your warehouse.
Why thickness matters more than appearance
Glass fails in transit because of shock, not because of load. A carton drops, the contents shift, and stress concentrates at thin sections. Wall thickness is the primary defence against that.
The trade-off is direct:
- Thin walls (1.5–2 mm) — cheaper per piece, lighter, elegant appearance, higher breakage in freight
- Medium walls (2.5–3.5 mm) — the practical sweet spot for container candles, handles stacking and palletisation
- Thick walls (4 mm+) — very durable, noticeably heavier, more expensive in both glass and freight
Every extra 0.5 mm of wall adds weight. Weight adds freight cost. This is why the thinnest jar that survives your shipping route is usually the most profitable one.
The hidden cost of breakage
Buyers calculate landed cost on the assumption that everything arrives. Real-world breakage on thin-walled glass in a 20ft container typically runs between 3% and 8% depending on packing quality and route. Add another 1–2% for glass that arrives intact but has micro-cracks and fails when the customer lights it.
Run the numbers on our8090, which is a medium-wall pressed jar at 250 g:
| Scenario | Arrival rate | Effective cost per unit |
|---|---|---|
| No breakage assumed | 100% | Base cost |
| 5% breakage | 95% | Base cost × 1.053 |
| 10% breakage | 90% | Base cost × 1.111 |
A 10% breakage rate turns a thin jar with a low ex-works price into the more expensive option per sellable unit. This is the calculation that should drive your specification, not the unit price on the quotation.
Weight is the number to watch
Weight matters twice: for freight and for handling. A 20ft container has a weight limit as well as a volume limit, and glass is dense. A 250 g jar fills a container with far less product than a 150 g jar of the same volume.
When you compare quotations, ask for the piece weight. A supplier who does not quote weight has probably not optimised anything, and you may be paying for glass that serves no purpose.
What specification to request
Send this in your RFQ:
\”Please confirm nominal wall thickness in mm at the body, base thickness in mm, and net piece weight in grams. Also state whether the jar is annealed and what your standard packing configuration is.\”
Annealing matters. Annealed glass has been slow-cooled to relieve internal stress. Non-annealed pressed glass can look identical and fail weeks later in a customer\’s home. Any supplier working at real volume anneals.
Practical rule
For container candles shipped by sea, use a body wall of 2.5 mm or greater with a base of at least 5 mm. Below that, increase your packing configuration or accept a higher breakage allowance in your pricing.
If you are unsure whether a jar you have quoted is thick enough for your shipping route, send us the specification and your destination. We will tell you what we would specify and why.