The present invention relates to a cellulose based electrically insulating composite material (1) in the form of a paper or pressboard, the material comprising cellulose fibres (2) and a thermoplastic polymer material (3), wherein the polymer material is arranged around and between the cellulose fibres such as to coat said fibres and/or bind said fibres to each other. The present invention also relates to a use of such a composite material for electrical insulation in an electrical device, as well as to a method of production of such a composite material.