Composites based on glass fiber reinforced low styrene emission polyester resins have been widely used over the last 10 years, in order to meet increasingly strict safety regulations, particularly in the pleasure boat industry. Previous studies of their mechanical properties suggested that although these resins are generally more brittle than traditional orthophthalic polyester resins this did not adversely affect the properties commonly used for quality control (short beam shear and tensile failure strength of mat reinforced composites). In the present paper results from a more detailed study of damage behaviour are presented. Tests include fracture toughness (K (Ic) ) tests on resins, fibre/matrix interface energy, detection of composite damage initiation in tension by acoustic emission, composite delamnation (G (Ic) and G (IIc) ), and low energy impact. Overall the results indicate that the low failure strain of low styrene emission resins results in significantly lower composite damage resistance.