An optimisation is carried out for extruding thermoplastics like Polyamide 6 (PA6) with natural fibre like flax or kenaf and FR. Extruder configuration is adjusted to obtain a stable process up to 22.5 wt% fibre. Mechanical testing shows just a decrease of 10% in strength and 15–25% in impact strength after the addition of 20% FR.V-0 rating is obtained by 20% FR according to UL94 test. The cone calorimetry shows a reduction in heat release rate HRR to 50% after the application of FR. Also higher share of mineral FR is found feasible keeping UL94 V-0 flame retardance level.