Washcoats with improved mass transfer properties are necessary to circumvent concentration gradients in case of fast reactions in liquid phase, e.g. nitrate hydrogenation. A highly porous, high surface area (180 m2/g) and thin washcoat of carbon fibers, was produced on a monolith support by methane decomposition over small nickel particles. Carbon fibers form a homogeneous layer less then 1 ¿m thin, covering the surface of the channels in the monolith. The fibers penetrated into the cordierite, which is suggested to cause a remarkable stability of the fibers against ultrasound maltreatment. The texture of the fibers is independent of both the thickness of the ¿-alumina washcoat as well as the time to grow carbon fibers.