noun
rate of expansion; expansion coefficient
Technical term used in physics, engineering, and materials science to describe how much a material expands per unit change in temperature or other conditions.
この金属の熱膨張率は非常に低い。
The thermal expansion coefficient of this metal is very low.
More specific term for thermal expansion coefficient; 膨張率 is a broader term that can refer to expansion due to any cause.
Compound of 膨張 (expansion) + 率 (rate, coefficient).