Only utensils of cloth, animal leather or bone, metal, wood or earthenware (and rabbinically, glass) can become impure, as it says "[Anything that they fall on...] any wooden vessel or garment or skin or sack...; and if any of them falls into any earthenware vessel...",¹ and it says "And every garment and every skin vessel and anything made of goats and any wooden vessel you shall purify... but the gold and the silver [the copper, the iron, the tin and the lead (shall be purified)]".² A non-metal utensil other than a container can only become impure rabbinically, except when it becomes impure by being sat on or lain on; and an earthenware utensil that is not a container cannot become impure at all, as it says "...into".^1,a

A utensil can only become impure after its fabrication is complete. A utensil part or a broken utensil that can no longer be used for its purpose (for earthenware: that can no longer be used as a container) cannot become impure; and if an impure utensil is broken it becomes pure (but rabbinically, if a metal vessel is later repaired it becomes impure again).^b

An earthenware utensil becomes impure only when a source of impurity enters inside it even if it does not touch it, as it says "...into"¹; but all other types of utensils become impure by touch even from the outside. Similarly, an earthenware utensil makes food and drink that are inside it impure even if they do not touch it, as it says "Everything that is in it becomes impure"³; and all types of utensils make food and drink impure by touch.^c