How Cosmetic Jars Are Made

Cream jars look simple and are not: they are assemblies of two to five moulded parts, and the interface between them determines whether the pack survives transport and daily use.

The parts of a jar

Part	Process	Function
Body (single or outer wall)	Injection moulding	Holds the formula, presents the brand
Inner cup (double-wall/refill)	Injection moulding	Formula contact, replaceable for refills
Lid (shell)	Injection moulding	Brand surface, closure
Lid insert or liner	Injection moulding, die-cut	Sealing surface
Gasket	Die-cut PE or silicone	Seals against the rim

Moulding sequence

1. Resin dried and colour verified against the approved sample
2. Body moulded, wall and thread measured; cycle parameters logged
3. Lid moulded; flatness checked for hot stamping or printing
4. Gasket die-cut to the body rim diameter
5. Assembly and closure torque verification
6. Decoration applied and adhesion tested
7. Final AQL inspection and packing

Thread and sealing design

The thread does not seal a jar — the sealing surface does. In most designs, the lid insert contacts the jar rim, and the gasket provides the barrier. Torque specification matters because:

• Too little torque: leakage in transit, product migration into the threads
• Too much torque: difficult opening, insert damage, thread stripping

We specify a torque range and verify it on the assembled pack, not on the parts separately.

Single-wall vs double-wall

Construction	Moulds	Assembly steps	Perceived quality	Recyclability
Single-wall	2 (body, lid)	Low	Thinner feel	Simplest if both are PP
Double-wall	3 (outer, inner, lid)	Medium	Thicker, heavier	Good if all parts are PP
Acrylic shell + PP cup	4+	High	Highest	Poor (mixed materials)
Refillable	4+	High, cycle tested	High	Best when reused

Quality checks that matter for jars

1. Dimension: rim diameter, thread pitch, lid depth
2. Closure torque range across a sample
3. Leak test inverted, filled to production level
4. Fill-height check against the inner lid rim
5. Stacking and carton drop test
6. Decoration adhesion (tape and solvent rub)

Why fill height is a packaging question

Most "jar lids leak" complaints are overfills. If the cream sits above the rim line, closing the lid forces product into the threads, which then migrates out. Fill to 90–95% of nominal capacity and keep the fill line 3–5 mm below the rim.