carbon - carbon composite brake discs are manufactured by processes that include the use of pan or pitch fibers and their combinations , combined with pitch , resin , or cvd / cvi matrix carbons . an additional process step is provided , in which a controlled amount of a carbon additive , such as carbon black and / or activated carbon , is infiltrated in to the bulk porosity of the composite prior to one or more of the densification cycles . typical methods of infiltration include use of a solution or suspension of the powdered carbon in water or solvent solution so as to uniformly distribute the particulates throughout porosity within the carbon fiber preform prior to one or more of the densification cycles . the presence of the activated carbon and / or carbon black additive , distributed throughout the carbon - carbon composite brake disc , facilitates the adsorption and retention of available moisture in the composite . in use , the moisture is released into friction films which form on the composite brake discs , so that their lubricating properties are obtained , for instance during cold taxi stops , thereby lowering wear rates .