A mineral sepiolite (magnesium silicate with microfibrilar morphology) was calcined at 325 degreesC and its behavior as filler for ethylene-propylene (EPM) compounds designed for electrical cable coating was studied. This calcined sepiolite is a material with good dielectric and physical properties and provides a reinforcing effect, increased when is treated with a coupling agent. The performance of this filler was compared to a commercial clay calcined at 1000 degreesC.