An effective utilization of exceptional high mechanical properties of nanofibres and nanoplatelets in composites is a challenging and currently unsolved issue in terms of significant improvement of the performance linked to dispersion homogeneity. Thus, the potential of the nanoparticles is not fully exploited and the composites fall short of the expectations regarding their mechanical property improvement. Our approach comprises an online process to 'heal' surface flaws and functionalize glass fibre surfaces. A nanometer-scale hybrid sizing or coating based on silane coupling agents and polymeric dispersions with multi-walled carbon nanotubes (CNT) and/or nanoclays, as mechanical reinforcement and environmental barrier layer, is applied to either E-glass fibres or alkali-resistant glass fibres (ARG). The nanostructured and functionalized glass fibres with low fraction of nanotubes or nanoclay (<1 wt% in sizing) show significant improvement in both mechanical properties and environmental corrosion resistance. We introduce a healing efficiency factor and conclude that the coating modulus, thickness and roughness are responsible for the mechanical improvement of fibres. The most remarkable mechanical strength improvement is found for glass fibres with nanotube surface modification, corresponding to the highest healing efficiency factor. No apparent decay in strength appears for nanoclay coated fibres subjected to alkaline attack, which indicates that the influence of moisture solvent uptake and concentration on mechanical properties decreases when the organoclay is dispersed in a coating polymer. Besides, nanocomposite coatings result in higher fibre/matrix interfacial adhesion, suggesting nanotube related interfacial toughening mechanisms. Overall, we show that the hybrid coating layer is essential for enhanced interfacial adhesion strength and improved mechanical properties of both the glass fibre reinforced concrete and thermoplastic matrix composites.