An amorphous material is a material that is not liquid at a temperature below the solidification temperature and has no crystalline structure. By cooling a liquid very rapidly (a cooling rate of 1,000,000 Kelvin per second), one can obtain an amorphous structure. In terms of physical properties, amorphous materials have, among other things, a lower softening temperature, lower specific gravity, higher flexibility and greater transparency than crystalline materials. Note that a material is always amorphous to a certain percentage. Thus, a material contains both amorphous and crystalline phases. A well-known example of an amorphous substance is the so-called metallic glasses.