Multi-Part Bottles: When Your Pack Is Four Pieces, Not One
A refill duo, a jar with a dosing insert, a tube with a collar and a decorative base — the pack is an assembly, and the mould budget follows the part count, not the bottle size. Here is how we plan it before anyone quotes.
Written by Joe Joo · 8PCK, Shantou
What "Multi-Part" Actually Means
Most packaging quotes assume one body and one closure. When the product is designed as an assembly, each element is its own mould, its own trial and its own tolerance stack — and the tolerance stack is where a beautiful render becomes a leaking sample.
| Part | Typical material | Process | What it decides |
|---|---|---|---|
| Body | PET, PETG, HDPE | Injection or blow | Holds the product; the wall carries the thread |
| Cap or insert | PETG, ABS, PP | Injection | Screws or sits inside the body |
| Collar | ABS, aluminium | Injection or turned | Carries a thread the body cannot hold |
| Base | ABS | Injection | Decorative; press-fit or screw |
| Seal | Silicone, EPDM | Standard or moulded | One per joint, in a defined groove |
Run the numbers before you ask a factory: mould cost estimator →
The Three Things That Move a Mould Budget
Part Count
Four parts ≈ four times one part. Size matters less than how many separate tools you need.
Thread Type
A thread that can be stripped off the core is low-cost. A closed thread needs an unscrewing mechanism: +30–45 % on that part.
Metal Finish
Gold and chrome are applied after moulding, but they need jigs and masking — and they change how the part is handled.
What We Check Before the Tool Is Cut
- Wall and draft. PETG at 2.5 mm is a slow cycle; 1.8 mm usually looks the same on shelf and costs less.
- Seal groove. An O-ring needs a defined groove depth and squeeze; a flat gasket needs a land width.
- Two threads on one joint. If both sides turn the same way, opening the cap can unscrew the body — one side goes left-hand.
- Through-bore or divider. A chamber that must stay separate until use needs a plug, a membrane or a valve — decide before tooling.
- Gate position. On a clear part, the gate shows. It goes at the base or under the collar, never on the shoulder.
Sealing, and How It Is Proven
We ask for the test, not just the word "airtight": vacuum hold (for example −0.3 bar for 30 seconds), a shake test with the real formula, or a drop test to the retail standard. The seal material follows the chemistry — silicone for most emulsions, EPDM where a solvent is involved.
Metal Finishes and One Honest Warning
Vacuum metallising gives the champagne-gold look on ABS at a moderate cost; electroplating is harder wearing and two to three times the price. Either can be attacked by an acid peel or a high-alcohol formula, so we ask for the pH and the solvent before the finish is chosen. If the formula is aggressive, the plated part moves to the outside and a PP liner goes inside.
Time and Confidentiality
- Drawing review — 3–5 days, with a DFM note back to you.
- Tooling — 30–40 days for a four-part assembly.
- T1 samples — 7–10 days, sent for fit and leak test.
- Production — 30–35 days after approval.
Your drawing stays yours. We sign an NDA before files are shared, we do not reuse a customer's tool for anyone else, and uploaded files are deleted on request — usually within 30 days.
What to Send for a Tooling Quote
- A drawing, a 3D file, or a photo of a pack you are matching
- How the volume splits between the parts, if there is more than one chamber
- Thread size, or the closure you intend to use
- Formula pH and solvent, for the seal and the finish
- First-run quantity, and the annual volume if you know it
- Target market — EU cosmetic packaging has its own declaration requirements
Send the Drawing. We Will Send Back the Mould Plan
Part-by-part tooling, the DFM notes, and what we would change before cutting steel.