Resin-rich mica tapes comprising one or more than one layer of mica paper and one or more than one layer of a nonmetallic inorganic fabric, in particular a glass fabric, which are pre-impregnated with an impregnation resin composition comprising an epoxy resin with more than one epoxy group, which is solid or semisolid at ambient temperature, a latent curing agent for said epoxy resin, about 5 to about 20% by weight of hexagonal boron nitride of a particle size (D50) of equal or less than about 3 μm, about 0.05 to about 1% by weight of a wetting agent and a suitable solvent which is removed after pre-impregnation of the mica tape with the impregnation resin mixture are useful to prepare electrical insulations with excellent thermal conductivity and dielectric dissipation factor.