Frequently Asked Questions (FAQs) About Sourcing PET Preforms

The necessity of a preform is dictated by the molding technology and the resin used:

• • Injection Stretch Blow Molding (ISBM) [Requires Preform]: This is the standard process for PET bottles. A preform is injection molded first to create a precise neck finish, then reheated and stretched. This process is essential for PET because the "stretch" aligns the molecules (biaxial orientation), creating the glass-like clarity and strength PET is known for.
• • Extrusion Blow Molding (EBM) [No Preform]: This process typically uses HDPE or PP (e.g., milk jugs, shampoo bottles). Instead of a preform, it uses a "parison"—a continuous tube of molten plastic extruded directly into the mold. EBM is preferred for opaque bottles or designs requiring integral handles, which preforms cannot easily accommodate.
• • In-Mold Labeling (IML): While IML is most common in EBM (parison-based), ISBM-IML is a premium niche. If you require IML on a clear PET bottle, you still need a preform, but your blow molder must use specialized robotic systems to insert the label into the mold alongside the heated preform.

This is known as the two-stage process (reheat stretch blow molding):

• • Heating: The preform is fed into a blow molding machine and heated to its specific glass transition temperature (approx. 100°C).
• • Stretching: A stretch rod physically extends the preform axially (lengthwise).
• • Blowing: High-pressure air blows the preform radially (widthwise) into the mold shape.

Successful sourcing requires matching the preform's "stretch ratio" to your final bottle shape to ensure uniform wall thickness.

Intrinsic Viscosity (IV) is a measure of the polymer's molecular weight, which directly correlates to the physical strength and stress-crack resistance of the final bottle.

• • Carbonated Soft Drinks (CSD): Require a higher IV (typically 0.80 – 0.84 dL/g) to withstand internal pressure and prevent stress cracking.
• • Still Water & Edible Oils: Can utilize a lower IV (typically 0.76 – 0.78 dL/g), which improves flow during injection molding and allows for lower melting temperatures, reducing energy consumption and acetaldehyde (AA) generation.

Acetaldehyde is a naturally occurring byproduct of PET thermal degradation during the melting process. While harmless, it can impart a fruity, chemical off-taste to water.

• • Sophisticated Sourcing: For premium spring water brands, ensure your supplier uses "Low AA" resins and optimized injection cycle times.
• • The Standard: Industry standard for water is typically < 2.0 ppm (parts per million), whereas CSD applications (which mask the taste) can tolerate higher levels (up to 9.0 ppm).

Both are standard finishes for carbonated beverages, but they represent different generations of lightweighting.

• • PCO 1810: The legacy "tall neck" standard (approx. 21mm height, ~5.1g). It is robust but material-heavy.
• • PCO 1881: The modern "short neck" standard (approx. 17mm height, ~3.8g). It offers significant resin savings (lightweighting) and faster cycle times without compromising seal integrity.
• • Migration Tip: Buyers switching from 1810 to 1881 must ensure their filling lines and cappers are re-tooled for the shorter finish height.

PET is hygroscopic. If preforms absorb ambient moisture during storage, they must be dried aggressively before blow molding, or they will suffer from hydrolytic degradation (loss of IV).

• • Defect Indicator: High moisture leads to "haze" or crystallinity in the bottle body and a brittle final product.
• • Storage Best Practice: Preforms should be stored in environments with controlled relative humidity and utilized within 6-12 months of production to ensure optimal blow-molding performance.

Yes. Advanced preform suppliers now offer up to 100% rPET content. However, sophisticated buyers should consider:

• • Color (L a b* values):** High rPET content can introduce a slight grey or yellow tint. Ask for "color-corrected" resins if optical clarity is paramount.
• • Processability rPET may require different heating profiles in the blow molder due to slightly different heat absorption rates (darker preforms absorb heat faster).
• • Regulatory Compliance: Ensure all rPET material is EFSA or FDA approved for food contact.

Lightweighting is not just about material savings. A shift from a 12g to a 9g preform for a 500ml bottle reduces:

• • Resin Cost: Direct savings on raw material.
• • Carbon Tax: Lower plastic volume reduces exposure to plastic packaging taxes (e.g., in the UK/EU).
• • Logistics: Lighter preforms allow for higher case counts per pallet, reducing shipping costs per unit.
• • Operational Considerations: Extreme lightweighting may compromise tactile integrity (the "feel" and rigidity of the bottle). To maintain rigidity at lower weights, you may need to implement liquid nitrogen dosing on your filling line to pressurize the bottle, which should be factored into your operational costs.

To source the correct preform, have the following specs ready:

• • Neck Finish: (e.g., PCO 1881, 29/25, 38mm Bericap).
• • Gram Weight: (Target weight based on your bottle volume and wall thickness requirements).
• • Resin Type: (Virgin PET, rPET, or specialized barrier resins).
• • ntrinsic Viscosity (IV): (Specific to your application—Water vs. CSD).
• • Color: (Clear, Light Blue, or custom Masterbatch code).

• • Resilux America *Industry Leader
  • • Location: Pendergrass, GA (USA) / Global HQ in Belgium.
  • • Specialties: A tier-one leader in barrier technology (ResiMax®) and high-volume preform supply. Vertical integration ensures unmatched consistency and agility.
• • Forpack
  • • Location: Shanghai, China.
  • • Specialties: Ideal for competitive global sourcing. They offer flexible MOQs, custom mold development, and a wide range of preforms for beverages and cosmetics. Exclusively works with PET, developing a strong expertise in PET preforms and bottles.
• • Precision Concepts International (PCI)
  • • Location: USA, Canada, and LATAM.
  • • Specialties: Specialists in high-precision injection molding.