Polyethylene Terephthalate

PET is the workhorse resin for clear packaging. It is a semi-crystalline polyester processed almost exclusively by injection stretch blow molding (ISBM), where an injection-molded preform is reheated and biaxially stretched into the finished bottle.

Biaxial orientation is what produces the properties buyers specify PET for. Clarity, dimensional stability, and gas barrier all develop during stretching. The unoriented preform has none of them, which is why stretch ratio governs PET performance more than the base resin does.

• Clarity: Over 90% light transmission, the closest of the commodity resins to glass.
• Gas barrier: Best CO2 and O2 barrier of the commodity resins, which is why carbonated beverages use it.
• Tensile strength: High, derived from biaxial orientation rather than the base polymer.
• Chemical resistance: Good against acids and most solvents. Poor against strong alkalis, which will attack it.
• Heat ceiling: Roughly 60°C. Standard PET is not a hot-fill or autoclave resin without heat-set or CPET processing.

Serums, toners, and tinctures. Beverages and supplements. Household and industrial chemicals where clarity sells the product. Cosmetic treatment bottles where a glass look is required at plastic cost and plastic weight.

In cannabis, PET works for non-terpene-bearing liquids. For terpene-heavy contents, confirm compatibility before tooling.

Process: Injection stretch blow molding (ISBM). We run 7 PET blow molding lines.

Shrinkage: 0.2-0.5%. Low and predictable, which is why PET holds neck finish tolerances well.

Drying is non-negotiable. Preform resin must be dried below 50 ppm moisture. Wet PET hydrolyzes in the barrel, producing acetaldehyde and a yellow cast. This is the most common cause of rejected PET runs.

Stretch ratios: Axial 2.5-3.5x, hoop 3.5-4.5x. Over-stretching produces pearlescence. Under-stretching leaves unoriented, weak material at the neck and base.

Gate: Center of the preform base. The gate vestige is visible on the finished bottle base and is normal.