Bitcoin value is backed by:

- blockchain - which will able bitcoin users to include messages in a globally distributed permanent ledger.
 Bitcoin's blockchain is probably the biggest database on Earth right now, there is nothing comparable and as widely distributed as blockchain.

- bitcoin's blockchain can also be used to confirm ownership of documents or identity of users.


- if we look at other commodities - most of them are only expensive and have value, because people decided and agreed that they are worth something

- bitcoin is useful (as currency, payment method, store value) and therefore is has value.

- but yes, in the end BTC value is determined by supply and demand.