These resin moulds are made from resin and so are hard moulds.  If using these for Polymer Clay please dust with talcum powder to help release the polymer clay (it may need poking with a toothpick to help ease it out).  If using with Art Clay Silver, there is no need to oil the mould, but dry the clay in the mould and once it is completely dry, turn the mould upside down and tap it – your moulded piece should fall out easily.