Insulator
/ˈɪnsəˌleɪtər/
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Definition
(noun) A substance that does not transmit heat (thermal insulator), sound (acoustic insulator) or electricity (electrical insulator).
Sentence Examples
Space is actually a good insulator because it is difficult to transfer heat to nothing.
It's a great insulator, keeping hot foods hot and cold foods cold.
CEFR Practice Quiz
Rubber is a good ____, which is why it is used to wrap electrical wires and prevent any shocks.