Incorporation of percolated carbon nanotubes (CNTs) into the composites interphase is a new approach for health monitoring of glass fibre (GF) reinforced composites.Unlike bulk nanocomposites, where the CNTs need to be dispersed and distributed throughout the whole matrix, this approach can be used in the same way for both thermoplastic and thermoset resins, as only the GF surfaces are modified by a matrix compatible CNT-sizing.