When plastics get too hot …

What happens if the limits are exceeded?

Kaprun | March 2026

Data sheets define operating limits.

What happens if these limits are exceeded?

In high-temperature applications, engineering plastics are often exposed to temperatures above the maximum service temperature specified in the data sheet — sometimes deliberately, sometimes due to design constraints. What happens inside the material usually remains invisible during operation. Only when components fail does it become clear that the limit had long been exceeded.

A brief high-temperature experiment makes this effect visible.

Several common engineering plastics — polyimide (PI), PTFE, PEEK, PA 6 G, and POM-C — were exposed to temperatures between 200 °C and 700 °C in an oven for exactly one minute. The aim was not standardized material testing, but rather a visual assessment of what actually happens under thermal overload.

The visible changes range from discoloration and swelling to the complete destruction of the component structure. However, the visual appearance is only the result of underlying processes. What is crucial is that plastics do not lose their technical properties abruptly, but gradually — often long before a component is externally perceived as damaged.

FAQ

Good to know

Up to what temperature can ZELLAMID 1500X (PEEK) be used?: Continuous service temperature: up to 260 °C
Short-term exposure to higher temperatures possible (e.g., under peak loads)
Up to what temperature can ZELLAMID 2200 (PI) be used?: Continuous service temperature: up to 300 °C
Short-term exposure to higher temperatures possible (e.g., under peak loads)
Is Plavis® the same as Vespel®?: Plavis® and Vespel® are both high-performance plastics based on polyimide, but they are manufactured by different companies. They differ in specific specifications and approvals. Therefore, they are not automatically interchangeable, but they can be technically compared depending on the application.
Is PI the same as TPI?: Polyimides (PI), such as ZELLAMID® 2200 (Plavis, Vespel), are thermosetting, non-meltable materials, whereas thermoplastic polyimides (TPI) are extrudable. This means that although both belong to the “polyimide family,” they differ fundamentally in their properties.

As soon as the specified service temperature is exceeded, the mobility of the polymer chains increases, while stiffness and compressive strength decrease and creep deformation begins. At the same time, oxidative and thermally induced degradation processes start to permanently alter the molecular structure. Electrical insulation properties deteriorate, coefficients of friction rise, and mechanical parameters lose their stability. From this point onward, data sheet values are no longer valid.

As the temperature continues to rise, the chemical decomposition of the polymer structure begins. The materials completely lose their characteristic properties and leave behind porous, brittle residues. Polyimide plays a special role here: its external shape remains intact for significantly longer, yet even in this case, mechanical and electrical properties gradually deteriorate once the specified temperature is exceeded. The stability is higher — but the physics remains the same.

The key insight is therefore simple and uncomfortable:

A plastic component may still “look fine” while it has already technically failed.

For design and mechanical engineering, this means that high-temperature applications leave no room for implicit safety assumptions. The maximum service temperature is not a recommendation, but a functional limit. Once it is exceeded, you leave the range of reproducible material properties.