The invention concerns an adhesive system comprising (a) a resin component comprising a urea based amino resin having an F/NH2 ratio from 0.3 to 0.65; (b) a hardener component comprising at least one acid, acid generating salt or acidic salt; and, (c) an aqueous polymer dispersion; wherein the adhesive system comprises no or less than 0.9 wt % of urea, based on the weight of the entire adhesive system, in addition to any urea present in the urea based amino resin. The invention further concerns a method of producing a wood based product, wood based products obtainable thereby and use of the adhesive system.