Fusibility is the ease with which a material will melt. Materials such as solder requires a low melting point so that when heat is applied to a joint, the solder will melt before the materials being soldered, i.e. high fusibility. On the other hand, firebricks used for furnace linings only melt at very high temperatures and so have the property of low fusibility. Such materials which only melt at very high temperatures are called refractory materials.