Abstract: Polyurethane gels are produced by converting a polyurethane system comprising (A1) one or more polyether alcohols of hydroxyl number 28 to 90 mg KOH/g produced primarily from propylene oxide added to a starter molecule of hydroxyl functionality between 2 and 4, (A2) one or more polyether alcohols of hydroxyl number 240 to 850 mg KOH/g produced primarily from propylene oxide added to a starter molecule of hydroxyl functionality between 2 and 4, (b1) one or more diisocyanates, (B2) one or more triisocyanates preferably produced by trimerisizing diisocyanates, (A3) at least one additive material fulfilling a prescribed function, and (A4) at least one additive material having a particle size in the range from 1 to 650 nm in the presence of one or more catalysts (A5) for forming polyurethane.