Physical Bitcoin coins tend to be preloaded with a fixed amount of BTC with the intention that its value cannot be spent as long as the private key remains hidden. This is usually achieved by using a tamper-evident seal.
The first of its kind, Bitbill, was shaped like a credit card, but most alternatives that followed were shaped like round medals. Mike Cadwell, a cryptocurrency enthusiast nicknamed “Casascius,” created the first of the popular Casascius physical Bitcoin in 2011.
Private keys were hidden under a peelable hologram, and when removed, it left a tamper-evident mark. When redeemed, the coin lost its digital worth. Since then, there have been several new coin manufacturers and some companies offer preloaded cards that contain a specified amount of crypto.
Physical Bitcoin is now primarily used as collectors’ items due to the inherent limitations of physical currency. One of Bitcoin’s key value propositions is to provide seamless transfers anywhere in the world — physical coins make that impractical.