The paper must be impregnated with Epoxy, Wax, Oil, or other suitable impregnate. It is still popular for high voltage and AC rated capacitors operating at lower frequencies. Paper is also wound with plastic dielectrics in combination dielectric capacitors. There are many different materials that can be used for the dielectric, I can't remember them all. The materials used in dielectric are called dielectric constants.
Some capacitors have several different constants mixed and used as the dielectric.