Infrared penetrates metal
Whatever doesn’t get reflected gets absorbed. Infrared lies between the visible and microwave portions of the electromagnetic spectrum covering a wide range of wavelengths – 700 nm to about 1 mm. This radiation is strongly absorbed by matter, and will not pass through. It does not pass through much. But not glass, or plastic. It’s behavior is the same as visible light.
Infrared penetrates metal. However, in general, on the red end of the visible spectrum, metals may be reflecting only about 90% to 95% – the rest penetrates the metal. Classical: no, metals cannot maintain a dipole. Light is basically a changing electromagnetic field. We relate infrared light to heat only when it interacts with matter and excites vibrational modes of motion of atoms in molecules. This is what is used in tv remotes. Once it’s in the metal, it is very quickly absorbed by the free moving electrons. Think of ir light like a heat signature for the most part.
Qm: metal band structures have transitions at an extremely wide range of energies. However, it can appear to pass through, because if you have a heat source behind the metal, the heat will pass through, and cause the outside of the metal to glow in ir.