A casting resin composition comprising or consisting of: (a) a monomer capable of forming a casting resin and/or coating upon polymerisation and (b) at least one thixotropic agent wherein said at least one thixotropic agent is a urea urethane and wherein said urea urethane is obtained or is obtainable according to the following steps: (a) providing a monohydroxyl compound of formula (I) R-OH (I) in which R is n-alkyl or isoalkyl containing 4 to 22 carbon atoms, cycloalkyl containing 6 to 12 carbon atoms, aralkyl containing 7 to 12 carbon atoms or a radical of the formula C m H 2m+1 (O-C n H 2n ) x - or C m H 2m+1 (OOC-C v H 2v ) x -, and m stands for an integer of from 1 to 22, n stands for an integer of 2 to 4, x for an integer of 1 to 15 and v means 4 or 5; (b) providing a diisocyanate compound of formula (II) OCN-[A]-NCO (II) in which A stands for a linear or branched alkylene radical having 2 to 10 carbon atoms and/or a toluylene radical; (c) reacting said monohydroxyl compound and said diisocyanate compound to form a pre-polymer; (d) reacting said pre-polymer with a diamine compound, said diamine compound being selected from the group consisting of (d1) compound (III) H 2 N-[B]-NH 2 (III) where B stands for a linear, branched and/or cyclic alkylene group having 2 to 12 carbon atoms; and/or (d2) compound (IV) H 2 N-(CH 2 ) a -Ph-(CH 2 ) b NH 2 (IV) in which a and b represent independent from each other integers from 1 to 5 and Ph stands for a phenyl radical, wherein said pre-polymer and said diamine are reacted in the presence of a surfactant. (a) a monomer capable of forming a casting resin and/or coating upon polymerisation and (b) at least one thixotropic agent (a) providing a monohydroxyl compound of formula (I) R-OH (I) in which R is n-alkyl or isoalkyl containing 4 to 22 carbon atoms, cycloalkyl containing 6 to 12 carbon atoms, aralkyl containing 7 to 12 carbon atoms or a radical of the formula C m H 2m+1 (O-C n H 2n ) x - or C m H 2m+1 (OOC-C v H 2v ) x -, and m stands for an integer of from 1 to 22, n stands for an integer of 2 to 4, x for an integer of 1 to 15 and v means 4 or 5; (b) providing a diisocyanate compound of formula (II) OCN-[A]-NCO (II) in which A stands for a linear or branched alkylene radical having 2 to 10 carbon atoms and/or a toluylene radical; (c) reacting said monohydroxyl compound and said diisocyanate compound to form a pre-polymer; (d) reacting said pre-polymer with a diamine compound, said diamine compound being selected from the group consisting of (d1) compound (III) H 2 N-[B]-NH 2 (III) where B stands for a linear, branched and/or cyclic alkylene group having 2 to 12 carbon atoms; and/or (d2) compound (IV) H 2 N-(CH 2 ) a -Ph-(CH 2 ) b NH 2 (IV) in which a and b represent independent from each other integers from 1 to 5 and Ph stands for a phenyl radical, wherein said pre-polymer and said diamine are reacted in the presence of a surfactant. (d1) compound (III) H 2 N-[B]-NH 2 (III) where B stands for a linear, branched and/or cyclic alkylene group having 2 to 12 carbon atoms; and/or (d2) compound (IV) H 2 N-(CH 2 ) a -Ph-(CH 2 ) b NH 2 (IV) in which a and b represent independent from each other integers from 1 to 5 and Ph stands for a phenyl radical, <EOS>