DESIGN FOR MANUFACTURING (DFM) GUIDE

Understanding Heat Resistance in Plastics

Choosing a plastic that can withstand your product's thermal environment is critical. This guide explains the key metrics and materials for high-temperature applications.

Key Metrics for Thermal Performance

"Heat resistant" can mean different things. Understanding these standard material properties will help you select the right plastic for the job.

Heat Deflection Temperature (HDT)

HDT is the temperature at which a standard plastic test bar deforms (bends) by a specific amount under a specific load. It is a useful metric for understanding a material's short-term ability to resist deformation under load at elevated temperatures. It is NOT a measure of a material's melting point.

Continuous Use Temperature

Also known as continuous service temperature, this is the maximum temperature at which a material can operate for its entire lifetime without significant degradation of its physical properties. This is a more practical, long-term measure of heat resistance and is often the most important number to consider for real-world applications.

Comparing Heat Resistant Plastics

Material	Typical HDT (approx.)	Continuous Use Temp (approx.)	Key Characteristics
ABS	88°C (190°F)	80°C (176°F)	Standard, good for consumer electronics.
Polycarbonate (PC)	138°C (280°F)	120°C (248°F)	High impact strength and clarity.
Nylon 66 (Glass-Filled)	245°C (473°F)	140°C (284°F)	High stiffness and wear resistance.
Ultem™ (PEI)	200°C (392°F)	170°C (338°F)	High strength, flame retardant (FST).
PEEK	152°C (306°F) (unfilled)	250°C (482°F)	Ultra-high performance, best chemical resistance.

Note: These values are approximate and can vary significantly based on the specific grade, fillers, and testing conditions.

Heat Resistance FAQ

Why is the HDT for Glass-Filled Nylon so much higher than its continuous use temperature?

This is an excellent observation. The glass fibers provide immense stiffness, which allows the material to resist bending under a short-term load at a very high temperature (the HDT test). However, long-term exposure to that same temperature will cause the base polymer to degrade and lose its properties. This is why continuous use temperature is often a more realistic guide for long-term applications.

How does adding glass or carbon fiber affect heat resistance?

Adding fillers like glass or carbon fiber almost always increases a material's Heat Deflection Temperature (HDT) because it makes the material much stiffer. It can also increase the continuous use temperature, but typically by a smaller margin. The fillers help the material hold its shape under load when it gets hot.

Which process should I use for a high-temperature prototype?

For prototyping with high-temperature plastics like PEEK or Ultem™, CNC machining is the most common and reliable method. There are also specialized 3D printing technologies (like high-temperature FDM) that can print with these materials, which can be a good option for creating complex geometries that are difficult to machine.