Composite sheet material

A composite sheet material comprising a fibrous sheet which is impregnated and/or is coated with a polyurethane elastomer;

• wherein said polyurethane elastomer comprises the reaction product of
• (A) a polymeric diol having a molecular weight of about 800-5000,
• (B) a mixture of organic diisocyanates comprising
• (a) about 2-70 mole % aliphatic diisocyanate not having a direct bond between an aromatic ring and an isocyanato group, and
• (b) substantially the balance comprising an aromatic diisocyanate having a direct bond between an aromatic ring and an isocyanato group;
• and
• (C) a chain extender comprising hydrazine and/or a derivative thereof having the formula (I):
• NH.sub.2 NHR (I)
• wherein R is a substituent selected from the group consisting of hydrogen, an alkyl group having 1-12 carbon atoms, an aryl group, an aralkyl group, an acyl group containing an amino group and groups having the formula --A--(ZA).sub.n --NHNH.sub.2, wherein A is a substituent selected from the group consisting of CO, CS and SO.sub.2, Z is a substituent selected from the group consisting of an alkylene group, an arylene group, an aralkylene group, --NH--, --NHNH--, --OYO-- and --NHYNH--, wherein Y is a difunctional organic group having 1-12 carbon atoms and n is 0 or 1;
• and
• said chain extender also including another chain extender having two functional groups comprising amino and/or hydroxy groups,
• wherein about 30-80% of the carbon atoms which are bonded to nitrogen atoms constituting the ureylene and/or urethane bonds of said polyurethane elastomer constitute a benzene and/or naphthalene ring skeleton, and wherein about 2-70% of the ureylene bonds of said polyurethane elastomer are formed by the reaction of aliphatic diisocyanate and hydrazine and/or its derivatives having the Formula (I).