When a shape-memory alloy is in its cold state (below M), the metal can be bent or stretched and will hold those shapes until heated above the transition temperature. Upon heating, the shape changes to its original. When the metal cools again, it will retain the shape, until deformed again.
With the one-way effect, cooling from high temperatures does not cause a macroscopic shape change. A deformation is necessary to create the low-temperature shape. On heating, transformation starts at A and is completed at A (typically 2 to 20 °C or hotter, depending on the alloy or the loading conditions). A is determined by the alloy type and composition and can vary between  and .