That does not conduct electricity or heat (or some other form of energy); that is a non-conductor. Also figurative.

Of a substance, body, etc.: not diathermic; allowing no transfer of heat.

= non-conducting, adj.

Not transmitting a form of radiation other than light, as sound, heat, or X-rays. Frequently with to.

Of a process or condition: that is one in which heat does not enter or leave the system concerned; of or relating to such a process or condition…

That insulates; spec. that does not conduct electricity or heat; that protects wires, or an electrified body, from conducting bodies. Also used with…

Of, pertaining to, or as insulation.

Electrically cut off from (the earth or other conducting bodies) by being surrounded with non-conductors. Also used with reference to heat and sound…