You can store your Polymesh (POLYX) in the free multi-coin that you receive when you sign up for an account with Cointree.
Within your multi-coin wallet, you can store POLYX and hundreds of other digital currencies listed on our exchange in your own wallet, such as popular long-term investments bitcoin and Ethereum.
Alternatively, you can store your Polymesh as cold storage in an external hardware wallet like a Ledger.