Is Magnesium Oxide used as insulator?

    Yes, it is. 

    It is used extensively as an electricalinsulator in tubular construction heating elements. There are several meshsizes available and most commonly used ones are 40 and 80 mesh per the AmericanFoundry Society. The extensive use is due to its high dielectric strength andaverage thermal conductivity. MgO is usually crushed and compacted with minimalairgaps or voids. The electrical heating industry also experimented withaluminium oxide, but it is not used anymore.

    It is also used as an insulator inheat-resistant electrical cable.