Can flexible plastics have reflective coating (vacuum metalized)?
There are many techniques for metal-coated polymers, as linked by permeakra Generally, vacuum deposition is an issue because the metal is hot. Cold deposition techniques (e.g., sputtering, ink coating) often work better.

Common, commercially-available materials include:


Pyralux - copper-coated polyimide from DuPont.
Mylar - DuPont's name for biaxially-oriented polyethylene terephthalate (BoPET)


As mentioned in other answers, adhesion is an issue, and to my knowledge, the processes to bind Pyralux and metabolized Mylar are proprietary.

Chemistry.About.com does mention vapor deposition of metals into Mylar, though.