The basic material for polycrystalline (also known as multicrystalline) cells is ultra-pure silicon. Liquid silicon for polycrystalline cells is first cast as ingots and then cut into wafers
which are 0.2 to 0.4 millimetres thick. The cells that result from this process are made up of many small single crystals, so-called crystallites, which are separated by grain boundaries. The pattern which results from the composition of different crystals is unmistakable, as is the bluish colour.