  Invisibility has attracted intensive research in various communities, e.g.,
optics, electromagnetics, acoustics, thermodynamics, etc. However, the most of
them have only been experimentally achieved by virtue of simplified approaches
due to their inhomogeneous and extreme parameters imposed by
transformation-optic method, and usually require challenging realization with
metamaterials. In this paper, we demonstrate an advanced bilayer thermal cloak
with naturally available materials first time. This scheme, directly from
thermal conduction equation, has been validated as an exact cloak rather than a
reduced one, and we experimentally confirmed its perfect performance
(heat-front maintenance and heat protection) in an actual setup. The proposed
scheme may open a new avenue to control the diffusive heat flow in ways
inconceivable with phonons.
