Pultrusion (profile extrusion) has traditionally been used for thermosetting plastics processing technology for thermosetting resins, because they can be easily the reinforcing fibre bundles. More recently, profiles made with thermoplastic matrix are also produced using this process. The secret is in situ polymerisation. The fibre bundle is impregnated with a low viscosity monomer which, during the profile drawing process, is by the addition of a catalyst and an activator.