Blockstream App uses the BIP39 standard—the most widely-adopted format in the Bitcoin industry—to generate your recovery phrase.
Recovery phrases generated using the BIP39 standard consist of either 12 or 24 words from a library of 2048 pre-specified terms. Blockstream App recovery phrases are 12 words by default.
As a hierarchical deterministic wallet, Blockstream App uses the BIP32 standard to derive the child keys for its wallet.
Although Blockstream App uses industry standards for recovery phrase generation, wallets created in Blockstream App using two-factor authentication (2FA) cannot be restored on other wallet software. This is due to the unique multisig security model used for 2FA Protected Accounts. In comparison, wallets that use Singlesig can be restored on most other wallet software (e.g. Electrum).
In order to restore BIP39 wallets created on other wallet software, you can select Restore from backup when creating a new wallet on Blockstream App.
Note: If you enter your recovery phrase from a 2FA account into a different wallet app that supports BIP39, the recovery phrase may be accepted by the app, but it will generate an empty single-signature wallet. Any transactions sent from or received to this wallet will be completely separate from your Blockstream App wallet.