There is provided a resin composition for producing a composite part, comprising: a) from 30 to 90 wt % by weight of the composition of an epoxy resin component; and b) from 5 to 50 wt % by weight of the composition of a curative component; wherein the epoxy resin component comprises N,N,N′,N′-tetraglycidyl-4,4′-diamino-3,3′-dimethyldiphenylmethane (M-TGDDM) in an amount of at least 30 wt % by weight of the epoxy resin component; and further wherein the curative component comprises one or more of a diaminodiphenyl sulfone, a diaminobenzophenone, a fluorene diamine, a methylene bis aniline, including hybrid methylene bis anilines, or a substituted diamine toluene. There is also provided the use of N,N,N′,N′-tetraglycidyl-4,4′-diamino-3,3′-dimethyldiphenylmethane (M-TGDDM) as a compression performance improving additive in a resin composition for producing a composite part. There are also provided curable composite components, cured composite components produced therefrom and the use of such components as aircraft components.