National Institute of Advance Industrial Science and Technology (AIST) have developed a new nanotechnology thin film material for a switchable mirror that can be switched between reflective and transparent states.The newly developed switchable thin film is made of an alloy of magnesium and titanium: this was successfully produced as a uniform layer on sheets of glass with the size of 60 x 70 cm and it shows switchable behavior. The switchable mirror consists of two layers of glass enclosing a cavity and coated on their interior surfaces with the alloy film. A gas that contains hydrogen at a low concentration of about 1% or oxygen at a concentration of about 20% is introduced to the cavity to activate the switching behavior. The thin film forms a reflecting mirror when it is applied to the glass, but it turns transparent when it is exposed to an atmosphere that contains hydrogen but no oxygen; it reverts to a reflective state when it is exposed to an atmosphere that contains oxygen but no hydrogen. The change between states is very impressive. The switchable windows that are actually used have a pair-glass structure with the thin-film applied as a coating on the inner sides of the two panes. Switching is achieved by introducing gas containing a low concentration of hydrogen (about 1%) or gas containing oxygen (about 20%) into the space between the panes. Small amounts of hydrogen and oxygen for use in the switching process can be readily generated by decomposition of water.