  Near the surface of any neutron star there is a thin heat blanketing envelope
that produces substantial thermal insulation of warm neutron star interiors and
that relates the internal temperature of the star to its effective surface
temperature. Physical processes in the blanketing envelopes are reasonably
clear but the chemical composition is not. The latter circumstance complicates
inferring physical parameters of matter in the stellar interiors from
observations of the thermal surface radiation of the stars and urges one to
elaborate the models of blanketing envelopes. We outline physical properties of
these envelopes, particularly, the equation of state, thermal conduction, ion
diffusion and others. Various models of heat blankets are reviewed, such as
composed of separate layers of different elements, or containing diffusive
binary ion mixtures in or out of diffusion equilibrium. The effects of strong
magnetic fields in the envelopes are outlined as well as the effects of high
temperatures which induce strong neutrino emission in the envelopes themselves.
Finally, we discuss how the properties of the heat blankets affect thermal
evolution of neutron stars and the ability to infer important information on
internal structure of neutron stars from observations.
