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What Is PET Preform Heating Temperature?
Before a PET preform becomes a bottle, it must pass through a heating stage that softens the resin without melting it. This step sets the foundation for stable bottles. If heating drifts too high or too low, walls will stretch unevenly, and the final bottle may crack, lean, or lose clarity.
In stretch blow molding, infrared lamps reheat the preform until the material becomes flexible enough to expand. Standard PET usually runs at 90–120 °C, while heat-resistant PET for hot-fill juices or teas needs higher zones, around 120–135 °C. The right range depends on preform weight, wall design, and your filling process.
For you as a buyer or production manager, heating temperature is not just a machine setting—it decides whether bottles stay clear, seal properly, and survive shipping. This is why asking suppliers for their recommended heating profiles and testing data is essential to avoid costly rejects and keep your supply chain reliable.
How Does Heating Temperature Affect Bottle Quality?
Impact on Transparency, Crystallization, and Color Stability
When PET is overheated past its crystallization point, chains tighten too much and the bottle turns cloudy or yellow. If heating stays stable, the resin stretches evenly, keeping bottles clear and glossy. For you, this means retail products look premium instead of “second grade.” When reviewing samples, always check: is the color uniform and does the surface stay bright?
Effects on Wall Thickness Distribution and Mechanical Strength
Wall thickness depends on how evenly heat reaches the preform before stretching. If one side is hotter, it thins out during blowing, leaving weak spots that collapse under stacking or carbonation. Proper heating gives balanced thickness, keeping bottles strong yet light.
| Application | Balanced Wall Result | Uneven Wall Result |
| Carbonated drink | Holds 0.3 MPa pressure | Bulges, leaks CO₂ |
| Mineral water | Stacks safely in pallets | Tilts, dents easily |
| Hot-fill juice | Keeps shape after 85 °C | Shrinks, wobbles |
Consequences for Sealing Performance and Shelf Life
The neck ring is especially sensitive. If heating distorts this area, caps fail to seal, letting oxygen in or carbonation out. With the right heating profile, caps lock tight, freshness lasts longer, and filling lines run without interruptions. When testing supplier samples, try twisting caps after storage—consistent sealing is proof of stable heating control.
For a hands-on QA checklist you can use on your line, see How to Check PET Preform Quality for quick tests on heating stability, wall balance, and neck accuracy.
What Problems Occur if Heating Temperature Is Not Controlled?
Overheating Issues – Yellowing, Shrinkage, and Stress Cracks
If a preform is exposed to too much heat, resin starts to degrade. You may notice bottles looking slightly yellow or hazy even before filling. Some sections shrink unevenly, pulling walls inward and creating stress lines. These tiny cracks often break later—on pallets, during capping, or worse, in a customer’s hands.
Underheating Issues – Quick Ways to Spot Brittle Bottles
When heating is too low, preforms resist stretching, leaving uneven thickness. You can spot it by:
- Bottles with one side stiffer or thicker than the other
- Bases that look lopsided or tilt on flat surfaces
- Walls that feel brittle and snap under a simple squeeze test
These signs mean the resin never softened enough, so the stretch ratio failed, and bottle strength is unreliable.
Production Risks – Why It Costs More Than You Think
Poor heating is not just about bad bottles—it disrupts your whole supply chain. Filling lines stop when caps don’t seal, distributors complain when pallets collapse, and every rejected batch means resin and transport costs wasted. If you are seeing repeated downtime or abnormal scrap rates, chances are the heating profile is not being controlled. That’s when working with a supplier who provides data-driven heating curves saves you both money and reputation.
How to Determine the Correct Heating Temperature for Your Application?
Differences Between Carbonated Drinks, Mineral Water, and Hot-Fill Juices
Every liquid puts different stress on a bottle. Carbonated drinks need precise heating to balance sidewall strength and base resistance, otherwise CO₂ escapes too fast. Mineral water is simpler, allowing slightly lower heating ranges without risking collapse. Hot-fill juices require special heat-resistant PET and higher reheating zones, otherwise bottles shrink after pasteurization.
Adjusting for Preform Weight, Neck Finish, and Mold Design
Here is a quick reference table showing how adjustments vary:
| Factor | What It Means | Practical Impact on Heating |
| Preform Weight | Heavier walls need longer heating | Avoids uneven stretch in thick zones |
| Neck Finish | Threads and tamper rings distort easily | Too much heat warps sealing surface |
| Mold Design | Airflow and cavity shape affect heat flow | Requires zone balancing to keep wall uniform |
Checking these three factors with your supplier ensures you don’t use a “one-size-fits-all” profile.
Role of Infrared Heaters and Temperature Zoning in Blow Molding
Modern blow molding machines don’t just heat everything the same. Infrared lamps are split into zones for the neck, body, and base. By asking your supplier how they set each zone, you can confirm whether bottles will stretch evenly and pass sealing tests. If the answer is vague, that’s a red flag—it means you may face rejects later on.
What Quality Practices Do Reliable Manufacturers Use?
Providing Preform Data Sheets with Recommended Heating Profiles
A good supplier does not hand you preforms and leave the rest to chance. Each batch should come with a technical data sheet showing drying instructions, heating ranges, and zone settings. This lets your team start production faster, with fewer rejects in the first runs. If your current supplier cannot provide this, you are probably losing resin and time without realizing it.
In-House Simulation and Testing for Hot-Fill and Cold-Chain Bottles
Every application has its stress points—hot-fill tea bottles face 85 °C pasteurization, while cold-chain juice bottles must survive transport at -20 °C. A professional manufacturer simulates these extremes before mass production. By verifying heating behavior under real conditions, we make sure bottles do not shrink, crack, or leak once they leave your plant.
OEM/ODM Support – Matching Heating Requirements to Custom Bottle Designs
When you want unique shapes, special neck finishes, or lightweight bottles, standard heating curves no longer work. We test preforms with your design, adjust temperature zoning, and fine-tune the heating curve. The result is a custom bottle that looks right on the shelf, seals tightly, and still runs efficiently on your filling line—without pushing up your costs.
Conclusion
Heating temperature is not guesswork—it is the fine line between smooth production and costly downtime. As you have seen, a few degrees decide whether bottles stay clear, strong, and shelf-stable or turn into rejects that drain your budget.
When you work with a professional PET preform manufacturer, you gain more than preforms. You get heating data sheets for fast setup, in-house testing that simulates your real filling conditions, and OEM/ODM support to align every heating curve with your product’s needs. This means fewer failures, lower resin costs, and a stable supply chain you can trust.
If you are planning your next packaging project, share your application details and budget with us. We will recommend the most suitable preform design and heating profile—cutting out waste and giving you reliable bottles at the best long-term value. Contact us today to secure consistent quality and protect your margins.
