High-temperature superconducting (HTS) cable systems delaminate at 175°C, necessitating a low processing temperature dielectric coating. A polymer nanocomposite can be prepared at temperatures below the HTS cable delamination temperature, mitigating this issue. The proposed polymer nanocomposite was composed of polymethyl methacrylate (PMMA) and impregnated with silicon dioxide (SiO2) to improve the dielectric performance of the base polymer. Dielectric breakdown testing shows a significant increase in the dielectric strength of PMMA/SiO2 composites at cryogenic temperatures when compared to room temperature testing. The increase is most significant across higher filler concentrations where the dielectric strength more than triples over room temperature values from 60-90 kV/mm to 290 kV/mm. The impact a colder testing environment has on dielectric performance makes PMMA/SiO2 nanocomposites a promising low temperature processing dielectric for adoption into HTS cable systems.