Temperature is also a variable that affects tissue processing. Heat has been used successfully in processing for decades to improve reagent and paraffin infiltration, as well as to improve turn-around time. An increase in temperature generally increases the rate of fixation and reagent infiltration, but if the temperature is too high it may effect tissue morphology. Introducing heat to tissue processing is suitable when the tissue thickness is less than 3 mm and the temperature is carefully controlled over short periods of time. During paraffin infiltration, the proper temperature is critical. Paraffin should be maintained at 2-4° C above the paraffin’s melting point. If tissue is exposed to overheated paraffin, tissue will over-harden. If the paraffin is below the target range, it may not infiltrate the tissue properly.