A low density polymer composition including a polymer component capable of being cured, a low density filler in an amount sufficient to reduce the density of the polymer and a thixotrope present in a sufficient amount to impart a sufficient viscosity and to inhibit separation of the filler from the polymer until after the polymer is cured. The resulting lightweight, filled polymer composition is a strong electrical insulator, has low shrinkage, a low coefficient of thermal expansion, low cured density and a soft filler that does not harden the polymer. Methods of preparing and using the low density polymer compositions are also disclosed.