A statistical experiment has been conducted to investigate the influence of silica fillers on the mobility of poly(vinyl chloride -co-vinyl acetate) molecules as reflected in glass transition temperatures. Measurement of glass transitions was made graphically from DSC curves. The data showed that the glass transition was affected by the presence of filler. The effect was dependent on the type and level of filler in the polymer. The filler was of either large or small particle size, or had had surface treatment to form trimethylsilyl groups. Significant interaction effects were found between filler types, filler level, and the level of polar vinyl acetate groups in the copolymer.