Salvatore Caltabellotta created a wallpaper made of fibreglass that incorporates a layer of copper(II) chloride. If the paper becomes moist, the colour pigments in it change and the wallpaper changes colour. The material can be used in various forms: wallpaper is the most obvious, but it can also be used as a folding screen.
Copper(II) chloride is a chemical compound with the chemical formula CuCl2. It is a light brown solid that gradually absorbs moisture to form a bluegreen dihydrate. Copper(II) chloride is the most common copper compound, after copper sulphate. As humidity rises, the copper(II) chloride turns a light-blue colour. As the humidity falls, it returns to its yellow/brown tint.