The present invention concerns a polymerizable thermoset composition, a polymerized thermoset, a process for the production of the polymerized thermoset as well as the use of the polymerizable thermoset composition for the production of lightweight construction components, preferably carbon fibre composite materials (CFC), and a lightweight construction component, preferably carbon fibre composite material (CFC), containing the polymerized thermoset. The composition comprises a) a polymerizable organic cyanate ester resin and b) a polymerizable aryl ethynyl-terminated polyimide. It can optionally comprise an allyl compatibilizer. The polymerized thermoset is in the form of non-covalently bonded interpenetrating networks, or, in the presence of the compatibilizer, in the form of a covalently bonded interpenetrating polymeric system.