The cooling time refers to the time required for the molten plastic inside the mold to cool and solidify, and accounts for most of the injection molding cycle time. The molten plastic is injected into the mold at the injection temperature and begins to cool as soon as it makes contact with the interior mold surfaces, kept at the mold temperature. When the material reaches the ejection temperature, the part can be safely ejected from the mold. Insufficient cooling time may result in a variety of part defects. The theoretical cooling time can be calculated from the thermodynamic properties of the plastic (such as the thermal diffusivity) and the maximum wall thickness of the part. However, a correction factor is often applied to account for how the mold geometry and cooling lines affect heat flow.