Which insulation is least likely to be used in high-temperature applications?

Thermoplastic insulation is characterized by its ability to soften when heated and solidify upon cooling. While thermoplastics offer good flexibility and resistance to certain chemicals, they typically have lower thermal stability compared to other types of insulation. In high-temperature applications, where persistent heat exposure can cause softening or deformation, thermoplastics may not maintain their integrity and performance.

In contrast, other insulation types like cross-linked synthetic polymers, varnished cambric, and rubber are designed to withstand higher temperatures and maintain their properties under thermal stress. Cross-linked synthetic polymers, for example, have a molecular structure that enhances their thermal resistance. Varnished cambric consists of layers of fabric impregnated with a high-temperature varnish, making it suitable for electrical insulation in high-temperature environments. Rubber, while it has specific limitations based on the type, can also be engineered to provide thermal stability for many electrical applications.

Therefore, when evaluating the insulation types for high-temperature applications, thermoplastic is least suitable due to its lower thermal resistance and potential for deformation under continuous heat exposure.