Polymer dispersed liquid crystals (PDLC) are dispersions of liquid crystal micro-droplets in a polymeric binder. Droplets appear as optically uniaxial spheres randomly oriented so that the material is optically isotropic. The application of an external electric field results in a reorientation of the liquid crystal and therefore in a switching of the sample from an opaque to a transparent state. Sample transmittance is also a function of the temperature. If the liquid crystal refractive index in the isotropic phase is equal to the one of the polymer, after the Nematic Isotropic transition the material is transparent. Therefore PDLCs show both thermo-optical and electro-optical effects. In this paper, we present a mathematical model able to describe the dependence of the sample transparency on the temperature, as a function of the applied voltage. We show the model accuracy by comparison with new experimental data that are briefly discussed.