Vibration isolator

A vibration isolator composed of low foam urethane elastomer having urethane bonds and a bulk density of 0.4-0.75 g/cm.sup.3, a permanent compression set of not more than 15%, a spring constant of at least 0.5 ton/cm, a tensile strength of at least 3.0 kg/cm.sup.2, an elongation of 20-500%, a fatique resistance, in terms of the amount of fatigue, of not more than 1.5 mm, and a closed cell forming ratio of at least 90%, and exhibiting excellent waterproofness and alkali resistance, said urethane elastomer being prepared by reacting a starting foamable liquid or urethane elastomer composition consisting essentially of

• (a) a polyether polyol having an average number of functional groups of 2.5-4.5 and a number average molecular weight of 2000-3500,
• (b) a vinyl monomer-grafted polyol having an average number of functional groups of 2.5-4.0 and the graft ratio is 4-20% by weight,
• (c) a liquid polybutadiene polyol having hydroxyl, terminal group(s), an average number of functional groups of 2.0-3.0 and a number average molecular weight of 2000-7000,
• (d) an organic polyisocyanate,
• (e) a chain extender
• (f) a blowing agent, and
• (g) a urethanation catalyst, in such ratios that the NCO index is within the range of 90-110, and the concentration of the chain extender, based on the total amount of the five components of (a), (b), (c), (d) and (e), is 0.3.times.10.sup.-3 to 1.5.times.10.sup.-3 mol/g.