One Pair of Rainproof Film for Car Rearview Mirror
Transparent Optical plastic with a waterproof nano coating that makes it slicker than ordinary glass.
A Silicone Glue backing means it can be removed and re-applied.
The nano coating also means that it won't fog up and get damaged by the Sun.
Note that these are sold as a pair (One pair is enough to do both the mirrors of one car)