bTokens are transferable, but users should do so with caution. bTokens are your receipt for supplied assets. If they are transferred, the rights to those supplied assets are also transferred. If you sent a bToken to your friend, your balance will decline and your friend’s balance will increase.
If a bToken has been used as collateral within Bitlend, an attempt to transfer will result in a failed transaction. This is required to maintain adequate liquidity levels within the protocol.