Base paste of polysulfide contains the following ﬁllers:
The base paste, is a polysulfide polymer that contains a multi-functional mercaptan (-SH) called a polysulfide polymer, a suitable filler (such as lithopone or titanium dioxide) to provide the required strength, a plasticizer (such as dibutyl phthalate) to confer the appropriate viscosity to the paste, and a small quantity of sulfur, approximately 0.5%, as an accelera-tor. The catalyst (or accelerator) paste contains lead dioxide, filler, and plasticizer as in the base paste, and oleic or stearic acid as a retarder to control the rate of the setting reaction. 
Lead dioxide is the component that gives polysulfide impression material its characteristic brown color. The terms catalyst and accelerator used here and with other impression materials are actually misnomers. Reactor is a more appropriate term for the reactions associated with polysulfide and other types of impression materials.
Key Concept:

Ref: Phillips Science of Dental Materials Ed 12 Pg 153
Silicon dioxide
Ferric chloride
Titanium dioxide
Barium sulfate