This Grater is composed of Corundum grains which appear in the family of ceramics and which are in the lohm scale at grade 9, the second hardest stone in the world after diamond (hardness 10). knowing that the natural Corundum for your information is sapphire and Ruby. Corundum is obtained by melting an aluminium Oxide and becomes a very high quality abrasive material. This chemical stone, to be used on wet feet, and not porous, allows all consumers to use it, including diabetics who do not expose themselves to micro-injuries which risk gangrening. It has 2 grains (large grain on one side and small grain on the other) and is washable with water. The design of its handle which adapts perfectly to the morphology of the hand makes its use easy.