A process of producing a fibre-reinforced composition comprising drawing a plurality of continuous filaments through a melt comprising a mixture of a thermoplastic polymer and a plasticizer for the polymer in the weight ratio between 1:4 and 99:1 of polymer to plasticizer, preferably in the weight ratio 1:1 to 19:1, the plasticizer being thermally stable at least up to the temperature of the melt and having volatility characteristics such that the plasticizer can be volatilized from the composition below the decomposition temperature of the composition but has a sufficiently low volatility at the temperature of the melt to plasticize the polymer in the melt and give a melt of reduced viscosity compared with the melt viscosity of the polymer alone. The process enables higher molecular polymers to be used in the pultrusion process and enables higher fibre contents to be achieved.