The invention relates to an electrically insulating composite material (1) comprising a polyepoxide matrix (2) of cycloaliphatic type or of diglycidyl ether type in a content of less than 40% by mass, from 20 to 75% by mass of one or several micrometric and/or mesometric filler(s) (3), and from 0.1 to 20% by mass of at least one ionic liquid (4), the masses being expressed relative to the total mass of the electrically insulating composite material (1). The invention also relates to a method for manufacturing such an electrically insulating composite material (1), as well as its use for an electrically insulating support (9) in a metal-enclosed substation (5).