A material that insulates, especially a nonconductor of sound, heat, or electricity.(noun)
A device that insulates.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "insulator" in a sentence
"A measure of whether a semiconductor most resembles a conductor or an insulator is given in the band gap - the amount of energy needed to produce moving charge-bearers in the form of electrons and "holes"."
"This forms an insulator which is not affected by heat or moisture."
"Although I am sure it would be hard for her to get brain freeze as air is an awesome insulator!"