Bitcoin is not a physical good that is susceptible to degradation. Rather, it is a digital good accessible only through cryptographic keys. As the only information needed to access bitcoin and authorise spends, a user’s bitcoin is therefore as durable as the medium that stores this information and/or manages these keys. Today, bitcoin wallets will typically provide users with a ‘seed phrase’ that encodes these keys. A seed phrase is normally 12 to 24 common words randomly chosen from a bank of 2,048 words, making the phrases easier to remember and maintain.
Many users store their seed phrase on paper. While this is a cheap and simple option, it leaves the seed phrase vulnerable to naturally degrading forces such as wear-and-tear, oxidation, water or fire. There is also a range of seed phrase storage products available for users wanting to store their seeds more securely. Stainless steel is a common, higher-grade available material, where each individual letter of a seed phrase can be punched into small plates and protected by a casing.
Indeed, seed phrases can be stored in any material capable of holding information, and the private keys required to spend bitcoin can therefore be as durable as the most durable materials. Note that the durability of keys is separate from the durability of the network and the protocol.