A method of tiling a two-dimensional plane using tiles with fivefold symmetry. Since this type of symmetry is not allowed in crystallography, two types of tile are needed, which are called ‘fat’ and ‘skinny’. Adjacent tiles have to obey certain matching rules. Penrose tiling, named after the British mathematician and physicist Sir Roger Penrose (1931– ), who put forward this idea in 1974, is the two-dimensional analogue of a quasicrystal.