We investigate the optical switching behavior of thermochromic layers, i.e., their spectral directionalhemispherical transmission and reflection as a function of temperature. On switching, thermochromic materials in layers of 1 mm provide a reduction of transmission in the optical region from 90% to 50%. We also performed directional-directional transmission and differential-scattering measurements and optical microscopy to derive structural information: a dramatic growth in the number and the size of particles is observed when the switching temperature is surpassed. These particles are formed by expulsion of water during the agglomeration of polymeric chains, which occurs when a characteristic switching temperature is surpassed. A multiflux-model permits predictions of the dependence of the directional-hemispherical transmission on the sample thickness and the angle of incidence.