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A systematic dielectric study over the frequency region from 0.06 to 300kHz has been carried out on butyl rubber loaded with one of six white fillers namely talc, calcium carbonate, dolomite, barytes, kaolin and silica in increasing quantities at room temperature. A low frequency loss term whose maximum lies around 104Hz for all samples is noticed and is attributed to Maxwell‐Wagner losses arising from the interfacial polarisation due to the presence of the ingredients added stepwise to raw rubber. These losses are found to increase by the addition of filler and the cause of this increase is interpreted.

A systematic dielectric study was carried out over a frequency range 60Hz-300kHz and at temperatures between 5 and 90°C on dehydrated castor oil mixed with different concentrations of styrene monomer to produce an insulating varnish. The volume resistivity was also studied. The results show that, when dehydrated castor oil is mixed with 10% styrene content by weight of the oil, epoxidised and then chemically treated with melamine resin and other additives, a varnish is produced with favourable electrical insulation properties.