Choosing the right PET bottle production method can save costs, ensure consistent quality, and speed up time to market. Many packaging engineers and brand owners struggle to choose between one-step and two-step blow molding. So what’s the real difference?
One-step PET bottle blowing combines injection molding and blowing in a single machine, making it ideal for small batches and custom shapes. Two-step PET blowing separates preform injection and blowing into two stages, allowing higher output, better cycle times, and lower costs for mass production.
Let’s break this down in more detail to help you make the right decision.
Outline
- 1 What Is the One-Step PET Blowing Process?
- 2 What Is the Two-Step PET Blowing Process?
- 3 Comparison Table: One-Step vs Two-Step Blow Molding
- 4 Which PET Blow Molding Method Is Better for Cosmetics?
- 5 Is One-Step PET Bottle Production More Expensive?
- 6 What Machines Are Used in Each Process?
- 7 Advantages and Disadvantages Summary
- 8 Conclusion
What Is the One-Step PET Blowing Process?
In the one-step process, preform injection, temperature conditioning, stretching, and blowing are performed sequentially in a single machine, often called an injection stretch blow molding (ISBM) system.
Key Characteristics:
- All-in-one machine
- No storage of preforms
- Ideal for custom packaging, complex bottle shapes, or limited production runs
- Typically uses 4–12 cavities
This process is popular in cosmetics, pharma, and premium personal care, where bottle uniformity and appearance matter more than unit price.
What Is the Two-Step PET Blowing Process?
In the two-step process, preforms are first manufactured and stored using an injection molding machine. Later, they are reheated and blown into bottles using a reheat stretch blow molding (RSBM) machine.
Key Characteristics:
- Separated preform production and blowing
- Preforms can be stored, transported, or sold separately
- Ideal for high-volume production, such as bottled water or beverages
- Machines run with 8–72 cavities for rapid output
This process is preferred by large-scale bottle manufacturers and beverage brands due to its speed and scalability.
Comparison Table: One-Step vs Two-Step Blow Molding
Feature | One-Step Process | Two-Step Process |
Machine | ISBM (Integrated) | Injection + Reheat Stretch Blow Machines |
Production Volume | Low to Medium | Medium to High |
Bottle Design Flexibility | High | Medium |
Energy Efficiency | Good (no reheat needed) | Lower (needs preform reheating) |
Mold Changeover Time | Longer | Shorter |
Output Speed | Slower | Faster |
Cost per Unit | Higher (small batch) | Lower (bulk production) |
Preform Inventory Needed | Not required | Required |
Common Use Case | Cosmetics, Pharma, Specialty Drinks | Bottled Water, Juice, Detergents |
Which PET Blow Molding Method Is Better for Cosmetics?
If your product line includes unique bottle shapes, short production runs, or frequent design changes, the one-step process is likely the better choice. It allows:
- More precise neck and shoulder design
- Shorter lead time from design to bottle
- Better surface quality (no dust from storage)
For high-volume products like toners or lotions in standard bottles, the two-step process offers better cost efficiency and faster delivery.
Is One-Step PET Bottle Production More Expensive?
Yes—but only in terms of unit cost. Here’s how the cost factors differ:
Cost Factor | One-Step | Two-Step |
Machinery Investment | Medium to High | High |
Mold Cost | High (more complex) | Lower |
Unit Cost (per 1k pcs) | Higher (small scale) | Lower (bulk) |
Operational Complexity | Lower (1 machine) | Higher (2 stages) |
That said, one-step is more cost-effective when dealing with small MOQs and design-intensive bottles.
What Machines Are Used in Each Process?
- One-Step: A single-stage ISBM machine such as ASB 70DPH, CHUMPOWER CPSB series, or Aoki systems
- Two-Step: Injection molding machine (for preforms) + reheat blow molding machine (e.g. SIDEL, Krones, Sacmi)
Large factories often combine several two-step lines for 24/7 production.
Advantages and Disadvantages Summary
✅ One-Step PET Blowing:
- ✔ Better for niche markets and flexibility
- ✔ Cleaner bottles (no storage phase)
- ✔ Faster for small runs
- ❌ Slower cycle time
- ❌ Higher cost per unit
✅ Two-Step PET Blowing:
- ✔ Ideal for high-volume runs
- ✔ Lower cost per bottle
- ✔ Easier mold changeovers
- ❌ More space and inventory required
- ❌ Preform contamination risk (if stored poorly)
Conclusion
Both PET blow molding processes serve different purposes. The one-step method offers design freedom and convenience for custom or cosmetic packaging, while the two-step method is unmatched for efficiency and mass production.
When choosing between them, consider your MOQ, design needs, lead time, and budget. For cosmetics, many premium brands rely on one-step systems to achieve the level of detail and quality their packaging requires.
Still unsure which fits your project? Let’s talk—I’m happy to help you evaluate your packaging goals and recommend the most efficient solution.