This paper presents a study of the delamination resistance Of unidirectional carbon fibre reinforced epoxy composites manufactured from prepreg for racing yacht mast applications. Fibre modulus has been varied from 290 to 640 GPa. Two manufacturing methods, oven cure under vacuum and autoclave, were used to produce samples. Results show that delamination resistance tinder mode I and mixed mode loading decreases as fibre modulus increases. The manufacturing route affects G, values by modifying interlaminar layer geometry but does not change the trend of lower toughness with increasing fibre modulus. For the pitch composites crack propagation is observed within the fibres, in addition to more usual matrix and interface cracking. For the very high modulus fibre composites it is no longer possible to measure the Gill,, fracture envelope with the MMB specimen, compression failure occurs before delamination. FE analysis and instrumented specimens have been used to define the limits to the current standard test method for these materials. (c) 2007 Elsevier Ltd. All rights reserved.