How does the resistance of a resistor change with rising ambient temperature?

The way a resistor reacts to changes in ambient temperature is determined by a property called its temperature coefficient. Some materials have a positive temperature coefficient, meaning their resistance increases as they get hotter, while others have a negative coefficient, meaning their resistance decreases with heat. Because resistors are manufactured using various materials and techniques—such as carbon composition, metal film, or wirewound—there is no single uniform behavior for all of them under thermal stress. Therefore, the direction and magnitude of the resistance change depend entirely on the specific component's temperature coefficient.