A mouldable thermoplastic material and process for making the same. The material comprises from 20% to 90% by weight of polypropylene, polyethylene or polyamide, from 80 to 10% by weight of glass fibre and from 0.05% to 15% by weight of an additive capable of coupling with the glass at a temperature in the range 180.degree. C to 300.degree. C and incapable of forming a homopolymer at that temperature. The additive is selected from oxalic acid and compounds containing the grouping ##STR1##