insulator(n = noun.substance) dielectric, nonconductor - a material such as glass or porcelain with negligible electrical or thermal conductivity;
is a kind of material, stuff
has particulars: bushing, mineral wool, rock wool, glass wool
Antonym: conductor
Derived form verb insulate₁

1.  One who, or that which, insulates. [1913 Webster]

2.  A substance or object that insulates; a nonconductor; as, polyurethane foam is a popular thermal insulator. [1913 Webster]

insulator, n.
1 a thing or substance used for insulation against electricity, heat, or sound.
2 an insulating device to support telegraph wires etc.
3 a device preventing contact between electrical conductors.