Hand laid up glass fibre reinforced isophthalic polyester resin and transfer moulded vinyl ester resin composites were subjected to environmental ageing. Gravimetric measurements were performed on laminate samples exposed to air and distilled water at 30 degrees C and 60 degrees C. Complementary porosimetry measurements on the original and fully aged samples indicated significant changes in the structure arising on ageing. Blistering showed that hydrolysis and de-bonding at the fibre-matrix interface occurred in polyester laminate to a greater extent at 60 degrees C than 30 degrees C. Leaching of monomer residues led to an anti-plasticisation effect in vinyl ester laminate. The influence of the fabrication method on the ageing behaviour is observed through porosity measurements on aged samples.