Thermal expansion describes how the size of materials changes with increasing temperature. There are three main types of thermal expansion: 1. Linear expansion is the increase in length per unit length for each degree rise in temperature. 2. Area expansion can be calculated from linear expansion. 3. Volume expansion also relates to linear expansion, with volume expansion being three times the linear expansion rate. Water is an anomaly as it contracts in volume from 0 to 4 degrees C before expanding normally at higher temperatures.