the polyurethane elastomers of the invention have an elongation of 600 percent or more as measured by astm d412 exhibit a tensile strength at break of at least 40 psi as measured by astm d 412 and exhibit a modulus of elasticity at 100 percent strain of less than 20 psi and at 300 percent strain of less than 40 psi as measured by astm standard d412 this low modulus of elasticity along with the good elongations and satisfactory tensile strengths at break are attained when employing a polyol prepared with the basic cesium or group ii alkaline earth metal catalysts to produce a degree of unsaturation ranging from 0 04 to 0 07 in another embodiment of the invention the elastomer prepared from the polyether polyols described herein have a modulus of elasticity which increases when strained from 100 elongation to 300 elongation by the word 34 increases 34 is meant that the as the elastomer is strained from an initial 100 elongation to 300 elongation the modulus of elasticity does not drop below the initial modulus of elasticity value as measured at 100 by more than 5 and the final modulus of elasticity measured as 300 elongation is higher than the modulus measured at 100 elongation in another embodiment of the invention the elastomer exhibits a ratio of a modulus of elasticity at 300 elongation to a modulus of elasticity at 100 elongation of at least 1 2.