Capillary wicking of liquids in natural fibrous reinforcements is a significant phenomenon in fibre-reinforced composites manufacturing through Liquid Composite Moulding (LCM) processes. Such phenomenon is however difficult to analyse due to heterogeneous, multiscale and variable fibrous medium during flow. Taking into account the fibre swelling, a modified Washburn’s model is proposed to predict the capillary rise of liquids in flax fibres. Particularly, swelling and wicking are studied at two different scales, i.e. elementary fibres and individual yarns. Swelling effects have been considered in the model and a modified Washburn’s theory has been developed. The proposed model satisfactory fits experimental results from capillary wicking tests, and hold for a 60% fibre volume fraction (Vf) of fabric on a relatively short duration while it fits well on a longer duration for lower Vf.