  Ar{\i}kan's polar coding, is by now a well studied technique that allows
achieving the symmetric capacity of binary input memoryless channels with low
complexity encoding and decoding, provided that the polar decoding architecture
is used and the decoding metric is matched to the true channel. In this paper,
we analyze communication rates that are achievable when the polar
coding/decoding architecture is used with the decoder using an incorrect model
of the channel. We define the `polar mismatched capacity' as an analogue of the
classical mismatched capacity, give an expression for it, and derive bounds on
it.
