Resin Transfer Moulding (RTM) processes used to manufacture high performance composite parts require an estimation of the fabric permeability and its variability. The value given to a constant intra-yarn permeability is thus a key parameter among many others studied in literature. To go further, the effect of variability into the intra-yarn permeability field onto 3D interlock fabric permeability is investigated. Reinforcements unit cells are modelled through material forming simulations which provide an intra-yarn fibre volume fraction (iy-FVF) field. The latter is used to locally compute an intra-yarn transversely isotropic permeability tensor field. Numerical simulations of dual-scale Stokes-Darcy coupled fluid flows between and within the yarns are performed with a monolithic approach by a Finite Element Method (FEM).