Single sourcing is cheaper right up to the day it is not. For first-world buyers manufacturing in Thailand, the question is not whether to dual source but which parts justify the duplication cost.
When a second source pays for itself
| Signal | Single source acceptable | Dual source recommended |
|---|---|---|
| Line-down cost | Low, buffer stock covers it | High — a stoppage costs more than the qualification |
| Tooling cost | High and specific | Low or transferable |
| Supplier concentration | You are 20-40% of their revenue | You are under 5% or over 60% |
| Regulatory exposure | Non-critical part | Medical, automotive, food contact |
| Demand volatility | Stable | Seasonal peaks above rated capacity |
The real cost of a second source
Duplicate tooling, a second qualification cycle, a second audit, split volume that pushes both suppliers off their best price break, and doubled quality-engineering time. Budget realistically: for most mid-volume programmes, the all-in premium is a few percent of annual spend in the first year and lower once both plants are stable.
Compare that premium against the cost of poor quality and against a single-plant shutdown. If one week of stockout wipes out the annual premium, the decision is made.
Volume splits that work
- 80/20 keep-warm — the secondary plant runs enough volume to stay qualified without losing your primary's price break. This is the default for most programmes.
- 60/40 competitive — used where price leverage matters more than absolute unit cost, or where capacity is genuinely tight.
- 50/50 regulated — used where a regulator or a customer contract requires two approved sites.
Never let a "second source" exist only on paper. A supplier who has not shipped in twelve months is not a second source; it is a phone number.
Geographic spread inside Thailand
Clustering both suppliers in the same industrial estate saves logistics and destroys the point of the exercise: flood, grid and port disruptions are regional. Pair an Eastern Seaboard plant with one in the Central or Northern region so a single event cannot take out both. Read our note on factory shutdown risk modelling for the numbers behind this.
Qualification without doubling your workload
- Reuse the same drawing pack, control plan and acceptance criteria for both plants.
- Run the same first-article protocol; do not soften it for the secondary.
- Audit both to the same standard using the factory audit checklist.
- Score both quarterly on the same supplier scorecard so the comparison is real.
- Keep tooling drawings and steel certificates in your own repository, not in each factory's server.
Cash implications
Two suppliers means two sets of payment terms, two safety stocks and slower inventory turns. Model the working-capital effect before you approve the split — see the Thailand sourcing cash cycle guide.
Frequently Asked Questions
Is dual sourcing worth it for low-volume parts?
Rarely. For low-volume, low-risk parts, a qualified buffer stock and a documented alternative material is cheaper than a full second qualification. Reserve dual sourcing for parts where a stoppage stops revenue.
How much extra does a second Thai supplier cost?
Expect duplicate tooling, one extra audit cycle and a loss of volume price break. For most programmes the first-year premium lands in the low single digits as a percentage of annual spend, falling once both plants are stable.
Will my primary supplier react badly to a second source?
Handle it openly. Framed as capacity assurance and business-continuity policy, most established Thai manufacturers accept it; several will propose their own sister plant as the backup.
Can both suppliers use the same tooling?
Only if the tool is transferable and you own it outright. Sharing one tool means you have capacity redundancy but no tooling redundancy — a tool failure still stops both lines.
How often should the secondary source ship?
At least one production run per quarter. Anything less and operators lose familiarity, and your first-article data goes stale.