Fire-retardant (FR) properties, including limiting oxygen index, peak rate of heat release, and smoke parameter have been measured and compared for unfilled and filled polyvinyl-chloride (PVC)-based cable formulations, containing 15 wt% amounts of uncoated and zinc-hydroxystannate (ZHS)-coated magnesium hydroxide (MH) and calcium carbonate (CaCO3) fillers at the same addition level. Of the uncoated fillers, M H was more effective at lowering flammability than CaCO3. When the ZHS coating was applied to MH and CaCO3, CaCO3 became the most effective additive at lowering PVC flammability and smoke output.