Through measurements of the low-temperature thermal conductivity and specific heat, we show that two classes of ferroelectrics can be distinguished. One class exhibits behavior typical of crystalline solids and the other displays behavior identical to that seen in structural glasses. We correlate these observations with measurements of the dielectric constant and optic index of refraction in the vicinity of the ferroelectric transition at Tc. Near Tc, those ferroelectrics with crystal-like thermal properties at low temperature exhibit normal behavior (i.e., a sharp ferroelectric transition) while those with glasslike thermal properties display a diffuse phase transition and a glassy polarization phase. The similarity to the elastic dipole glass (KBr)1-x(KCN)x is discussed. © 1985 The American Physical Society.