Flax fibres were thermally treated, to prove that in the same manufacturing conditions, modifying wetting and swelling properties of fibres changes the flow during LCM processes and thus could enhance the final material health of composite parts. Swelling of untreated and treated fibres was measured with optical and tensiometric methods proving that the thermal treatment increases the dimensional stability of flax fibres. A methodology to minimise the dispersion of contact angle values was also developed, and surface energy components of untreated and treated fibres were then determined in the frame of the Owens and Wendt theory. It was evidenced that the thermal treatment makes fibres less hydrophilic. Composite half plates reinforced with untreated and treated flax fabrics were then simultaneously manufactured by Liquid Composite Molding (LCM) process (resin infusion) and finally, a reduction of porosity was observed in composites reinforced with treated flax fabrics. (C) 2017 Elsevier Ltd. All rights reserved.