The general rule is resistivity increases with increasing temperature in conductors and decreases with increasing temperature in insulators. … Thus when temperature goes up, resistance goes up. For some materials, resistivity is a linear function of temperature.
Heating a metal conductor makes it more difficult for electricity to flow through it. These collisions cause resistance and generate heat. … Heating the metal conductor causes atoms to vibrate more, which in turn makes it more difficult for the electrons to flow, increasing resistance.