and or propoxylated castor oil castor oil ethoxylated and or propoxylated tallow oil and 4 tallow oil the mentioned flexibilizers may be used individually or in the form of mixtures particularly preferred are difunctional polyoxyalkylene glycols difunctional polyester polyols tallow oil and castor oil typical organic polyisocyanates which can be used for the subject invention include for instance aromatic polyisocyanates such as 2 4 and 2 6 toluene diisocyanate as well as their commercially available isomer mixtures 2 2 39 2 4 39 and 4 4 39 diphenylmethane diisocyanate as well as their isomer mixtures particularly those of 2 4 39 and 4 4 39 diphenylmethane diisocyanate and mixtures of the isomeric diphenylmethane diisocyanate and polyphenyl polymethylene polyisocyanates crude mdi instead of the pure polyisocyanates or polyisocyanate mixtures modified aromatic polyisocyanates such as carbodiimide urethane and or isocyanurate group containing polyisocyanates based on the above mentioned aromatic polyisocyanates may also be used preferably used are the commercially available optionally modified diphenyl methane diisocyanates crude mdi and their mixtures the quantity ratio in which the polyol mixture and the organic polyisocyanates are brought to reaction can be varied within wide ranges for instance in a ratio of hydroxyl to isocyanate groups of 1.