a process which includes comminuting a first thermoplastic material , e . g . polypropylene , reinforced with short glass fiber . 100 parts by weight of the comminuted material are mixed with 11 - 43 parts by weight of chips of a second thermoplastic material , which is reinforced with long glass fiber . the melts of the two thermoplastic materials should be mutually mixable . the mixture is subjected to thermoplastic forming .