Elastic and glassy polymers are normally considered as homogeneous disordered materials with unimodal (statistical) distribution
of elementary free volumes. In this work, we discuss the results of our positron annihilation lifetime (PAL) measurements
for a number of elastic and glassy polymers, where observations of the two long-lived ortho-positronium components in the
PAL spectra and irregular (nonlinear) variations of annihilation characteristics in the vicinity of glass transition temperature
reveal structural heterogeneity of these systems. The conclusion is confirmed by measurements of thermo-stimulated luminescence,
thermo-mechanics and mobility of penetrants.