A curable polyisocyanate composition comprising at least one or more polyisocyanate compounds, at least one or more trimerization catalyst compounds, at least one or more aldehyde compounds wherein the aldehyde compound is selected from compounds with the structure R—CHO wherein CHO is an aldehyde group and R is a hydrocarbyl group selected from an alkyl, alkenyl or aryl having 1-50 carbon atoms, preferably 1-20 carbon atoms, and at least one or more compounds selected from compounds which comprise a carboxamide group having the structure —CO—NH2 and/or from compounds which comprise a group having the structure —CO—NH—CO—.