Thermoplastics Vs Thermoset Plastics: Which Is Better for Custom Injection Molded Parts?

Introduction

Have you ever tried to “un-bake” a cake? Once it’s baked, there’s no going back. This is exactly how thermoset plastics behave—they permanently cure and form strong chemical cross-links, giving them excellent heat resistance and dimensional stability. In contrast, thermoplastics are like chocolate: you can melt them, pour them into molds, cool them, and then melt them again to reshape. This simple distinction defines how these two types of polymers perform in custom injection molding.

What Are Thermoplastics?

Thermoplastics are polymers that soften when heated and harden when cooled. This property allows them to be re-melted and reshaped multiple times, making them ideal for injection molding processes that demand flexibility, precision, and high-volume production.

Common Thermoplastic Materials for Injection Molding

For a detailed comparison of material properties and recommended applications, see our Thermoplastic Materials for Injection Molding

Thermoplastic Processing Considerations

• Mold Temperature & Cooling: Proper cooling channels prevent warping and ensure dimensional accuracy.

• Cycle Time: Thermoplastics typically allow fast cycles (<1 minute per shot), supporting high-volume production.

• Part Geometry: Ideal for complex features like snap-fits, living hinges, thin walls, and multi-cavity molds.

• Recyclability: Scrap material can be reground and reused, supporting environmentally friendly manufacturing.

• Limitations: Continuous exposure to high temperatures(>200°C) can cause deformation or softening.

Thermoplastics are widely used in consumer electronics and automotive components due to their versatility, recyclability, and ease of processing. Below are two representative examples that highlight why thermoplastic materials are chosen for these products.

For instance, the automotive bumper made from PP+EPDM relies on thermoplastic flexibility and impact resistance—features that thermosets cannot provide. It can be efficiently injection molded, easily painted, and remains durable under UV and weather exposure while being recyclable at the end of its life.

Similarly, the charger housing made from flame-retardant PC/ABS combines rigidity, heat resistance, and smooth surface quality with high manufacturing precision. Unlike thermosets, it allows fast production, aesthetic finishes, and controlled recyclability—perfectly fitting modern consumer electronics.

What Are Thermoset Plastics?

Thermoset plastics start as liquid or malleable polymers and permanently harden through a chemical curing process. Unlike thermoplastics, once cured, thermosets cannot be re-melted or reshaped. This curing forms strong chemical cross-links that provide high heat resistance, rigidity, and chemical stability.

Common Thermoset Materials

Thermoset Processing Considerations

• Curing: Requires precise temperature and dwell time to fully cross-link the polymer.

• Mold Design: Must account for shrinkage, flash, and undercuts; air ejection or special coatings may be necessary.

• Part Geometry: Thin walls, ribbed sections, and embedded inserts require careful flow analysis.

• Cycle Time: Longer than thermoplastics (typically 2–5 minutes per shot), due to curing requirements.

• Performance: Excellent dimensional stability under high temperature and chemical exposure.

Thermosets excel in electrical insulation, automotive high-temperature components, industrial parts, and medical devices.
For example, circuit breakers and wall switch housings are typically made from thermoset materials such as phenolic resin (PF) or bulk molding compound (BMC). These materials provide exceptional heat and arc resistance, dimensional stability, and electrical insulation, which thermoplastics cannot match in such high-voltage environments. Unlike thermoplastics, once cured, thermosets maintain their shape even under prolonged heat and electrical stress, ensuring long-term safety and reliability.

Thermoplastics vs Thermosets — Key Differences

Chocolate vs Baked Cake Analogy

Think of thermoplastics as chocolate: melt it, pour into a mold, cool it, and you can melt it again to create another shape. Thermoplastics allow repeated processing and recycling, which is excellent for high-volume manufacturing.

Thermosets, on the other hand, are like a baked cake: once it’s baked, it cannot return to batter. You get permanent strength and stability, ideal for high-temperature and high-stress applications, but recycling or reshaping is impossible.

Performance Comparison Table

Production Process Differences

Thermoplastics

• Pelletized material is melted, injected, cooled, and ejected.

• Mold cooling channels regulate shrinkage and cycle time.

• Suitable for multi-cavity molds and large production volumes.

Thermosets

• Pre-polymer or compound mixed, heated, injected, and cured chemically.

• Mold heating ensures complete curing; cycle times are longer.

• Requires careful design for flash, shrinkage, and part ejection.

Understanding these differences helps manufacturers balance speed, precision, and durability, ensuring each part meets performance and quality requirements.

When to Choose Each Material

Choose Thermoplastics When:

• Rapid cycle times and low unit cost are required.

• Lightweight and impact-resistant parts are needed.

• Recycling or reprocessing of material is desired.

• Complex geometries or tight tolerances are involved.

Choose Thermosets When:

• High-temperature performance and dimensional stability are      critical.

• Chemical resistance or electrical insulation is required.

• Long-term mechanical integrity is needed in harsh environments.

How Material Selection Impacts Mold Design

Thermoplastic Molds

• Cooling channels regulate shrinkage and cycle times.

• Multi-cavity molds support high-volume production.

• Standard ejector pins handle part release.

Thermoset Molds

• Heated molds or temperature-controlled platens ensure complete curing.

• Air-assisted ejection or specialized coatings may be required.

• Mold design must consider shrinkage, undercuts, and wall thickness variations.
  

conclusion

In the world of custom injection molding, the difference between thermoplastics and thermoset plastics is more than chemistry—it’s strategy. Thermoplastics offer speed, flexibility, and recyclability, making them the top choice for high-volume production and intricate part geometries. Thermosets, on the other hand, bring unmatched heat resistance, rigidity, and stability, perfect for demanding applications where performance cannot be compromised.

Ultimately, the “right” material depends on your product’s environment, function, and lifecycle expectations. Whether your priority is precision, durability, or sustainability, understanding the trade-offs between these two material families helps you make informed decisions that optimize both performance and cost.

At Alpine Mould, we often start prototypes with thermoplastics, then move to thermosets for high-performance production. This strategy reduces risk, accelerates validation, and optimizes mold cost.

At Alpine Mould, we guide clients through material selection with data, experience, and transparent recommendations . Whether you need thermoplastic molds, LSR molds, or complete custom plastic parts production, our team helps balance cost, performance, and manufacturability from day one.

Contact us today to discuss your part design — we’ll help turn your ideas into production-ready reality.