A thermosetting composition comprising (a) 97 to 40 percent by weight of at least one bis(dihydrobenzoxazine) prepared by the reaction of an unsubstituted or substituted bisphenol with at least one unsubstituted position ortho to each hydroxyl group, formaldehyde and a primary amine; and (b) 3 to 60 percent by weight of at least one bisphenol selected from hydrochinone, resorcinol, catechol, or from bisphenols of formula II, wherein R 4 is hydrogen, dialkylamino; alkylthio; alkylsulfonyl; C 1 -C 18 alkyl; C 1 -C 18 alkoxy; C 1 -C 18 alkoxyalkyl; C 5 -C 12 cycloalkyl that is unsubstituted or substituted by one or more C 1 -C 6 alkyl groups or C 1 -C 6 alkoxy groups; C 6 -C 12 aryl that is unsubstituted or substituted by one or more C 1 -C 6 alkyl groups or C 1 -C 6 alkoxy groups; or C 7 -C 13 aralkyl that is unsubstituted or substituted by one or more C 1 -C 6 alkyl groups or C 1 -C 6 alkoxy groups; X 2 is a direct bond or a bivalent bridging group selected from -O-, -S-, -S -, -S 2 -, -C -, -NR 3 -, -O-C -, -O-C -O-, -SO 2 -O-, -O-SO 2 -O-, -NR 3 -C -, -NR 3 -C -O-, -NR 3 -C -NR 3 -, -NR 3 SO 2 -, -NR 3 -SO 2 -O-, -O-SO 2 NR 3 -,-NR 3 SO 2 -NR 3 -, -P (OR 3)O-, -OP(OR 3)O-, - P(OR 3)-, -P(OR 3)-, -P(R 3)-, -O- P(R 3)-O-, C 1 -C 18 alkylen, C 2 -C 18 alkyliden, C 3 -C 12 cycloalkyliden, -Si(OR 3) 2 - and -Si(R 3) 2 -; and R 3 is H or C 1 -C 12 alkyl, C 5 - or C 6 -cycloalkyl, C 5 - or C 6 -cycloalkyl-methyl or -ethyl, phenyl, benzyl or 1-phenyleth-2-yl wherein the percent by weight refer to the total amount of components (a) and (b), with the proviso that (a) and (b) add up to 100 percent by weight; (c) a protonic acid curing catalyst; and (d) optionally other components. (a) 97 to 40 percent by weight of at least one bis(dihydrobenzoxazine) prepared by the reaction of an unsubstituted or substituted bisphenol with at least one unsubstituted position ortho to each hydroxyl group, formaldehyde and a primary amine; and (b) 3 to 60 percent by weight of at least one bisphenol selected from hydrochinone, resorcinol, catechol, or from bisphenols of formula II, wherein R 4 is hydrogen, dialkylamino; alkylthio; alkylsulfonyl; C 1 -C 18 alkyl; C 1 -C 18 alkoxy; C 1 -C 18 alkoxyalkyl; C 5 -C 12 cycloalkyl that is unsubstituted or substituted by one or more C 1 -C 6 alkyl groups or C 1 -C 6 alkoxy groups; C 6 -C 12 aryl that is unsubstituted or substituted by one or more C 1 -C 6 alkyl groups or C 1 -C 6 alkoxy groups; or C 7 -C 13 aralkyl that is unsubstituted or substituted by one or more C 1 -C 6 alkyl groups or C 1 -C 6 alkoxy groups; X 2 is a direct bond or a bivalent bridging group selected from -O-, -S-, -S -, -S 2 -, -C -, -NR 3 -, -O-C -, -O-C -O-, -SO 2 -O-, -O-SO 2 -O-, -NR 3 -C -, -NR 3 -C -O-, -NR 3 -C -NR 3 -, -NR 3 SO 2 -, -NR 3 -SO 2 -O-, -O-SO 2 NR 3 -,-NR 3 SO 2 -NR 3 -, -P (OR 3)O-, -OP(OR 3)O-, - P(OR 3)-, -P(OR 3)-, -P(R 3)-, -O- P(R 3)-O-, C 1 -C 18 alkylen, C 2 -C 18 alkyliden, C 3 -C 12 cycloalkyliden, -Si(OR 3) 2 - and -Si(R 3) 2 -; and R 3 is H or C 1 -C 12 alkyl, C 5 - or C 6 -cycloalkyl, C 5 - or C 6 -cycloalkyl-methyl or -ethyl, phenyl, benzyl or 1-phenyleth-2-yl wherein the percent by weight refer to the total amount of components (a) and (b), with the proviso that (a) and (b) add up to 100 percent by weight; R 4 is hydrogen, dialkylamino; alkylthio; alkylsulfonyl; C 1 -C 18 alkyl; C 1 -C 18 alkoxy; C 1 -C 18 alkoxyalkyl; C 5 -C 12 cycloalkyl that is unsubstituted or substituted by one or more C 1 -C 6 alkyl groups or C 1 -C 6 alkoxy groups; C 6 -C 12 aryl that is unsubstituted or substituted by one or more C 1 -C 6 alkyl groups or C 1 -C 6 alkoxy groups; or C 7 -C 13 aralkyl that is unsubstituted or substituted by one or more C 1 -C 6 alkyl groups or C 1 -C 6 alkoxy groups; X 2 is a direct bond or a bivalent bridging group selected from -O-, -S-, -S -, -S 2 -, -C -, -NR 3 -, -O-C -, -O-C -O-, -SO 2 -O-, -O-SO 2 -O-, -NR 3 -C -, -NR 3 -C -O-, -NR 3 -C -NR 3 -, -NR 3 SO 2 -, -NR 3 -SO 2 -O-, -O-SO 2 NR 3 -,-NR 3 SO 2 -NR 3 -, -P (OR 3)O-, -OP(OR 3)O-, - P(OR 3)-, -P(OR 3)-, -P(R 3)-, -O- P(R 3)-O-, C 1 -C 18 alkylen, C 2 -C 18 alkyliden, C 3 -C 12 cycloalkyliden, -Si(OR 3) 2 - and -Si(R 3) 2 -; and R 3 is H or C 1 -C 12 alkyl, C 5 - or C 6 -cycloalkyl, C 5 - or C 6 -cycloalkyl-methyl or -ethyl, phenyl, benzyl or 1-phenyleth-2-yl wherein the percent by weight refer to the total amount of components (a) and (b), with the proviso that (a) and (b) add up to 100 percent by weight; (c) a protonic acid curing catalyst; and (d) optionally other components.