Positive temperature coefficient of resistivity (PTCR) behavior of poly(methyl methacrylate) PMMA/silver (Ag)-coated glass bead composites has been investigated with reference to the conventional PMMA/carbon black (CB) composites. The PMMA/CB composites showed a sudden rise in resistivity (PTC trip) at 115 degrees C, close to the glass transition temperature (T(g), 113 degrees C) of the PMMA. However, the PTC trip temperature (92 degrees C) of PMMA/Ag-coated glass bead composites was appeared well below the T(g) of PMMA. The room temperature resistivity and PTC trip temperature of the composites were also very much stable upon thermal cycling. Addition of 1 phr of nanoclay increased the PTC trip temperature of PMMA/CB composites to 120 degrees C, close to the T(g) (118 degrees C) of PMMA/clay nanocomposites, while PMMA/clay/Ag-coated glass bead nanocomposites showed the PTC trip at 98 degrees C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between PMMA and glass beads played a key role that led to a disruption in continuous network structure of Ag-coated glass beads even at a temperature well below the T(g) of PMMA. The decrease in dielectric permittivity of PMMA/Ag-coated glass bead composites on increasing frequency indicated possible use of the PTC composites as dielectric material. POLYM. ENG. SCI., 51:1780-1790, 2011. (C) 2011 Society of Plastics Engineers