The use of carbon nanotubes (CNTs) as filler material for the mechanical reinforcement of plastics requires an effective surface functionalisation in order to allow the integration of CNTs into the molecular structure of the matrix. Some of these additives have an effect on the chemical structure, thus changing the mechanical properties of the investigated epoxy. This paper examines the extent of matrix reinforcement achieved through the addition of CNTs, functionalised CNTs and a variety of additives. It is shown that the mechanical improvements of the matrix are due mainly to the modification of the chemical curing reaction and only to a small degree to the CNTs.