Abstract The manufacture of negative Poisson’s ratio (auxetic) composites, containing inherently auxetic phases is rare and has been confined to relatively low modulus composite systems with stiffnesses several orders of magnitude below those of structural composites. This paper presents the use of an auxetic double helix yarn that is used to produce a unidirectional fibre composite with both relatively high stiffness (4 GPa) and negative Poisson’s ratio (−6.8), at 30% fibre volume fraction, compared to other auxetic composites. This is the first structural auxetic composite to be produced using carbon fibre and importantly it was produced using standard manufacturing techniques and therefore is potentially applicable in a variety of engineering applications.