noun
heat resistance; heat-resisting property
Technical term used in materials science, engineering, and product specifications to describe the ability to withstand high temperatures without degrading.
この容器は耐熱性に優れている。
This container has excellent heat resistance.
耐熱性の高い素材を選んでください。
Please choose a material with high heat resistance.
耐火性 means 'fire resistance', the ability to withstand fire or high heat from flames, often used for building materials. 耐熱性 is broader and includes resistance to heat in general, not necessarily fire.
Compound of 耐 (たい, 'resist'), 熱 (ねつ, 'heat'), and 性 (せい, 'property/nature'). A straightforward Sino-Japanese technical term.