Home › PET Preforms: Neck Finishes, Weights & Quality
A PET preform is the small injection-molded test-tube shape that a blow molding machine stretches into a bottle. Its weight decides the bottle's stiffness; its neck finish decides which closure fits — and neither can be changed after molding.
The neck finish is molded to a standard so that a closure fits. For example, a 43 mm neck is used for foamer pump bottles, while smaller finishes such as 20 mm and 24 mm suit sprayers and small bottles. The finish is already crystallized (heat-set) at the thread so it keeps its shape during blowing.
| Preform weight | Suitable bottle | Note |
|---|---|---|
| ~12 g | Small bottles (100–250 ml) | Light-weighted, cost-sensitive lines |
| ~27 g | 500 ml household and personal care | Common for 43 mm foamer-pump bottles |
| Heavier grades | Larger or pressure-rated bottles | Stiffness and drop strength increase with weight |
Weight and bottle volume must be matched to the blow mold. A preform that is too light for the mold's bottle design produces thin walls at the shoulder and base; too heavy wastes material.
The preform's length, weight and neck finish must match the blow mold's bottle design. If you already have a mold, send its bottle drawing and target weight; if you are starting fresh, the preform and mold can be quoted together so both are designed for the same bottle.
It is the neck's diameter standard. A 43 mm finish is commonly used for foamer pump bottles; the pump, the preform and the blow mold must all be specified to the same finish standard.
Heavier preforms produce stiffer bottles with better drop strength; lighter preforms save material but the bottle design must compensate. Weight and mold must be matched, or walls end up thin at the shoulder and base.
The neck thread area is deliberately crystallized (heat-set) so it keeps its shape during blow molding. A clear or translucent neck indicates insufficient crystallization and is a quality defect.
Yes. Send the mold's bottle drawing and target weight so the preform is supplied to match the mold — an unmatched preform causes uneven wall distribution.