at least two layers of reinforcement fibers impregnated with a first curable matrix resin comprising one or more thermoset resins; and

an interlaminar region formed between adjacent layers of reinforcement fibers, the interlaminar region comprising soluble polyimide particles and insoluble thermoplastic particles embedded in a second curable matrix resin that is the same as or different from the first curable matrix resin in composition,

wherein

the soluble polyimide particles are fully dissolvable in the second matrix resin at a curing temperature of the second curable matrix resin and the insoluble thermoplastic particles remain as discrete particles in the interlaminar region at said curing temperature,

the curing temperature of the first and second curable matrix resins is in the range of 140° C. to 220° C.,

the soluble polyimide particles are formed from an amorphous polyimide, which is a reaction product of an aromatic dianhydride and an aromatic diamine containing an aliphatic or a cycloaliphatic structure, and

the polyimide particles are present in an amount of no more than 2.5% by weight.