A semipreg that can be cured/molded to form aerospace composite pails -including rocket booster casings. The semipreg includes a fibrous layer and a resin layer located on one side of the fibrous layer. The resin layer includes an epoxy component that is a combination of a hydrocarbon epoxy novolac resin and a trifunctional epoxy resin and optionally a tetraiunctional epoxy resin. The resin matrix includes polyethersulfone as a toughening agent arid a thermoplastic particle component.