the invention relates to a liquid acrylic syrup for impregnating a fibrous substrate . the invention especially relates to a viscous liquid syrup mainly containing methacrylic or acrylic components . the invention also relates to a method for producing such a syrup . the invention relates further to a process for impregnating a fibrous substrate or long fibers with said viscous liquid syrup . the invention also relates to a fibrous substrate preimpregnated with said syrup , which is useful for the production of mechanical or structured parts or products . the invention also relates to a production method for producing mechanical or structured parts or items and to three - dimensional mechanical or structured parts produced by said method . the invention applies to the production of mechanical parts or structural elements made of impact - resistant thermoplastic composite material .