the correct name is "Casascius" and it is not offline storage, it is a physical bitcoin and this type is not exactly meant to be used for storage. they are designed to be used as "collectibles" for those who like having collections such as hobbyist, etc.
they also are meant to have a fixed balance (the balance that was originally put in that key) and remain that way meaning you should never spend from that key (which requires physically revealing the private key) because it makes stop being a collectible.