Polybutylene Terephthalate，commonly referred to as PBT plastic, is a high-performance thermoplastic material that is widely used in PBT injection molding applications. It is well-regarded for its outstanding heat resistance, excellent dimensional stability, and low moisture absorption. These core properties make it a preferred choice for manufacturing automotive components, electrical connectors, and various consumer and industrial parts through the injection molding process.

If you'e exploring materials for your next injection-molded project, PBT injection molding offers a strong balance of performance and cost-efficiency. This guide will provide everything you need to know about working with this versatile engineering plastic, including:

Contents

1. Common Grades and Key Features of PBT for Injection Molding

2. Applications of PBT Plastic in Injection Molding

3. Advantages and Limitations of PBT

4. Design Guidelines for PBT Injection Molded Parts

5. Process Parameters and Practical Tips for PBT Injection Molding

Common Grades and Key Features of PBT for Injection Molding

PBT is widely used in injection molding, and different grades vary in their focus on strength, heat resistance, processability, and regulatory compliance.

To meet a broad range of application needs, suppliers offer a variety of formulations — from standard grades to flame-retardant, UV-resistant, and medical-grade options.

The following table summarizes the most common PBT grades, representative brands, key properties, and typical applications, providing a useful reference for your material selection and product design.

Grade Type	Representative Brands	Key Features	Applications
Unfilled   PBT	Celanex® 2002, Crastin® S600F20	High flow, good electrical insulation, easy to   mold	Connectors, precision parts, small electronics
30% GF   Reinforced PBT	Celanex® 3300, Valox® 420SEO	High rigidity, dimensional stability, heat   resistance	Automotive parts, pump housings, motor   enclosures
Flame-Retardant   PBT	Crastin® FR530, Valox® 357	UL94 V-0 rated, flame-resistant	Electrical housings, power modules
UV-Stabilized   PBT	Crastin® S610F20U, Valox® DR51	UV-resistant, outdoor applications	Outdoor lighting, solar components
FDA/Medical   PBT	Celanex® MT Series, Valox® 310	FDA/ISO10993 compliant, low extractables	Medical devices, food processing equipment
Impact-Modified   PBT	Valox® 325, Crastin® HR5330	High impact resistance, low temperature   toughness	Industrial plugs, shock-resistant parts

Applications of PBT Plastic in Injection Molding

Injection-molded PBT is widely used in electrical, automotive, home appliance, and medical applications.

Electronics and Electrical

Typical applications: 

• Connectors, 

• switches

• relays

• sockets

• electrical housings

• keyboard covers

Function: Ensures stable performance of components in high-temperature environments and provides electrical insulation

Automotive Manufacturing

Typical applications: 

• Wiper brackets

• headlamp bezels

• motor housings

Function: To ensure stable operation of the device in high-temperature environments and provide electrical insulation.

Home Appliances

Typical applications: 

• External and internal parts of irons

• hair dryers

• rice cookers

Function: Maintains product stability and safety under high-temperature and high-humidity conditions.

Medical Devices

Typical applications:

• Injection pens

• autoinjectors

• dry powder inhalers

• dose counters

Function: Offers safety, durability, and heat resistance for medical components designed for human contact.

Advantages and Limitations of PBT

Advantages of PBT Injection Molding

One of the most important features of PBT plastic molding is its excellent dimensional stability. With a low moisture absorption rate (approximately 0.1–0.2%) and a controllable shrinkage range, Polybutylene Terephthalate molding maintains high dimensional accuracy even in humid environments. This makes it an ideal choice for tight-tolerance applications.

High Mechanical Strength

When reinforced with glass fibers, PBT exhibits high tensile and flexural strength, making it suitable for structural components in automotive and industrial applications. This property is especially important in PBT injection molding for parts that require both strength and reliability.

Heat Resistance

PBT offers continuous service temperatures of around 120–140°C. Glass-filled grades can achieve heat deflection temperatures (HDT) exceeding 200°C, making them a strong candidate for under-the-hood automotive parts or heated appliance housings. Such thermal performance is critical in any PBT injection process where long-term heat resistance is required.

Electrical Insulation

PBT features high dielectric strength and a high Comparative Tracking Index (CTI), providing excellent electrical insulation. This makes it a preferred material for electrical and electronic connectors, switch housings, and insulating components — all essential elements in modern PBT plastic molding applications.

Chemical Resistance

PBT offers good resistance to a variety of solvents, oils, greases, and weak acids, making it durable in chemically aggressive environments. This durability adds long-term value in both consumer and industrial applications.

Processability and Surface Finish

Due to its fast crystallization rate, PBT injection molding allows for shorter cycle times and excellent mold detail replication. In addition, it delivers a smooth surface finish, often eliminating the need for secondary processing. These characteristics make it a standout material in any PBT molding design guide focused on efficiency and aesthetics.

Limitations and Alternatives of PBT

Although PBT injection molding offers excellent dimensional stability, strength, and electrical insulation properties, it also has some limitations. You should consider these limitations when selecting.

Limited Hydrolysis Resistance:

PBT tends to degrade in high-temperature and high-humidity environments.

Alternative: 

Use PPS or LCP for better hydrolytic stability under such conditions.

UV Sensitivity:

Standard PBT is not UV-resistant and may degrade or discolor when exposed to outdoor environments.

Alternative: 

Choose UV-stabilized PBT grades or PA66 with UV additives for outdoor use.

Brittleness of Unfilled Grades:

Virgin, unreinforced PBT can be brittle, especially under impact or at low temperatures.

Alternative: Use impact-modified PBT or PC/ABS blends to improve toughness.

Higher Cost:

Compared to commodity plastics like PP or ABS, PBT is relatively more expensive.

Alternative: 

If performance requirements are lower, ABS or PP can serve as more cost-effective options.

By understanding these limitations and considering appropriate alternatives, you can make more informed decisions regarding the performance, durability, and cost-efficiency of your PBT injection molding parts.

Design Guidelines for PBT Injection Molded Parts

When designing parts with PBT injection molding（插内链）, engineers must take into account the material’s characteristics—such as high flowability, low moisture absorption, and crystallinity—to ensure optimal dimensional stability and mechanical performance. Below are

key design recommendations to improve molding efficiency and part functionality.

Wall Thickness

Recommended range: Typically 1.2–3.0 mm, depending on part size and geometry.

Uniformity: Maintain consistent wall thickness to avoid sink marks, warpage, or uneven cooling.

Thick sections: If thicker areas are necessary, consider using hollow sections, reinforcing ribs, or tapered transitions to reduce defects.

Ribs and Bosses

Ribs	Bosses
Thickness   should not exceed 60% of adjacent wall thickness	Place bosses on or near ribbed or   reinforced areas
Height should   generally be no more than 2.5–3× the wall thickness	Avoid direct perpendicular connection   to walls
Use smooth   transitions to the main wall with radii of 0.25–0.5 mm	Use angled transitions or gussets to   better distribute stress

Draft Angles

Recommended draft angle: 0.5°–1° for smooth surfaces; increase to 2° or more for textured surfaces.

Avoid zero-draft designs, especially with glass-filled PBT, which is more prone to sticking and ejection issues.

Radii and Corners

Avoid sharp corners: All internal and external transitions should use generous radii.

Typical guidelines:

External corners: ≥ 0.5 mm

Internal corners: ≥ 0.6 × wall thickness

(Attention: Rounded corners help reduce stress concentration and improve fatigue strength.)

Shrinkage Considerations

Typical shrinkage rate: 0.7–2.2%, depending on glass fiber content and orientation.

Structural impact:

Ribs, uneven wall thickness, and asymmetrical designs can increase warpage risk.

Mismatch between fiber orientation and flow direction may also lead to internal stress and deformation.

Process Parameters and Practical Tips for PBT Injection Molding

Preprocessing

Drying Treatment: PBT materials are prone to hydrolysis at high temperatures. Before processing, they must be dried at 120°C for 6–8 hours or 150°C for 2–4 hours, ensuring moisture content is below 0.03%.

Molding Parameters for PBT Injection Molding

Parameter	Recommended Range
Barrel Temperature	240–280°C; for glass fiber   reinforced PBT: 230–260°C
Mold Temperature	40–60°C for unfilled PBT; 60–80°C   for reinforced PBT
Injection Pressure	Typically 60–100 MPa; 80–100 MPa for   glass-filled PBT
Injection Temperature	Since the decomposition temperature   of PBT is 280°C, maintain 235–245°C
Injection Speed	Use a high injection speed due to   PBT’s fast cooling rate
Melt Temperature	225–275°C; recommended setting:   250°C
Screw Speed	Should not exceed 80 r/min;   generally 25–60 r/min; for complex parts: ~30 r/min
Back Pressure	Typically 10%–15% of the injection   pressure

Runner and Gate Design

Runner: Circular runners are recommended to ensure efficient pressure transmission.

(Empirical formula: Runner diameter = part thickness + 1.5 mm)

Gate:

Various gate types can be used. Hot runners are acceptable but must be carefully managed to avoid material leakage or degradation.

Gate diameter should be 0.8t–1.0t (t = wall thickness). For submarine gates, a minimum diameter of 0.75 mm is recommended.

Molding Cycle Time

Typically ranges from 15 to 60 seconds, depending on part size and design.

Conclusion

Understanding the specific design and processing requirements of PBT injection molding is essential to achieving consistent part quality and long-term performance. From proper material drying and precise temperature control to optimized runner and gate design, every step plays a critical role in successful production.

At Alpine Mold, we specialize in high-precision injection molds and molded parts using engineering plastics like PBT. With over 20 years of experience serving global clients in the automotive, electronics, medical, and consumer sectors, we are confident in our ability to support your most demanding projects.

Looking for a reliable partner in PBT injection molding? 

Get in touch with Alpine Mold today to explore how our expertise can help bring your product vision to life.