What type of materials do not expand when exposed to heat?

Passive materials are those that do not undergo significant physical change, such as expansion, when exposed to heat. This characteristic is crucial in various applications, including firestop systems, where maintaining the integrity of fire barriers is essential during a fire event. Passive fire protection materials, such as certain types of concrete, masonry, and non-combustible insulation, are designed to withstand high temperatures without expanding, ensuring that they continue to perform effectively even under extreme conditions.

In contrast, other types of materials, such as active, reactive, or composite materials, may exhibit expansion or other changes when subjected to heat. Active materials can react to temperature changes by changing shape or size. Reactive materials often change properties or react chemically with other substances when heated. Composite materials can have differing responses to heat based on their composition, which often includes both expanding and non-expanding elements. Hence, passive materials are the most reliable choice when it comes to not expanding under heat.