Polymers and particulate composites are being increasingly used in heat insulation and dissipation applications. Accurate measurement of their thermal diffusivity is critical for reliable thermal designs. Commercially available methods, developed for homogeneous materials, rely on localized heating of small specimens. The localized area may not truly represent the bulk in heterogeneous materials like particulate composites. This paper presents a simple inexpensive technique to measure the thermal diffusivity of polymers and particulate composites. An analytical solution for the temperature distribution in a slab is obtained incorporating actual boundary conditions employing modified Angstrom's method. From the resulting implicit relationships and temperature measurements at three easily accessible surfaces, thermal diffusivity is estimated. Proposed method circumvents prominent issues faced like heat loss due to imperfect contact by employing non-contact heating/cooling. This avoids special specimen preparations such as use of graphite coating and gold sputtering. Estimated thermal diffusivity for four polymeric solids and two particulate composites compare well with values from Laser flash method and literature. © 2019 Elsevier Ltd