Carbonaceous materials are widely applied as materials that absorb electromagnetic radiation, whether in the form of carbon fibers, nanotubes and graphene. In this work the carbon fiber from raw material textile polyacrylonitrile was used in two distinct forms, felt and particulates. The carbon fiber felt samples showed real and imaginary permissiveness about four times higher than those in particulate form and also a reflection of up to 93% of the incident radiation. The study of the particulate fibers was carried out with particles of sizes smaller than 25um and 25-53um and embedded in an epoxy resin matrix in two concentrations of mass, 25% and 50% of carbon fiber. The best attenuation occurred for samples with particulate size 25-53um, where the concentration of 50% attenuated until 60% and the samples with 25% carbon fiber concentration until 75%.