Millennium 4 carbon composite sole the millennium 4 carbon composite sole features injected carbon fibre in a matrix of nylon providing more rigidity than a standard nylon sole the millennium 4 carbon composite sole is also more durable completely non water absorbent and mechanically stable meaning its less susceptible to changes in stiffness resulting from ageing prolonged usage and changes in temperature or humidity an anti slip toe insert and replaceable polyurethane heel pad are inco