The aim of this study was to determine water sorption, water solubility, dimensional change caused by water storage, residual monomers, and possible cytotoxic effects of heat-polymerized carbon-graphite fibre-reinforced composites with different fibre loadings based on methyl methacrylate/poly(methyl methacrylate) (MMA/PMMA) and the copolymer poly (vinyl chloride-co-vinyl acetate).