If you've ever tried to use Bitcoin in a DeFi protocol on Ethereum, you've run into the problem that wrapped tokens solve. Blockchains don't natively talk to each other, so a Bitcoin can't just appear on Ethereum. Wrapped tokens are the workaround; and they're one of the most important (and underappreciated) pieces of infrastructure in crypto.
What Are Wrapped Tokens in Simple Terms?
A wrapped token is a cryptocurrency that represents an asset from one blockchain made compatible with another blockchain, backed 1:1 by the original asset locked in a smart contract or custodial reserve. For example, Wrapped Bitcoin (WBTC) is an ERC-20 token on Ethereum backed by real BTC, allowing Bitcoin holders to participate in Ethereum DeFi without selling their Bitcoin. Wrapped ETH (WETH) makes native ETH compatible with the ERC-20 standard used by most DeFi protocols.
Why Wrapped Tokens Exist
Each blockchain is its own isolated world. Ethereum doesn't know what's happening on Bitcoin. Solana doesn't know what's happening on Ethereum. They have different rules, different token standards, and different virtual machines. A Bitcoin is a UTXO on the Bitcoin network; it simply cannot exist as an ERC-20 token on Ethereum.
But the DeFi ecosystem on Ethereum is enormous; lending, borrowing, trading, yield farming — and Bitcoin holders want access to it without selling their BTC. Similarly, developers want liquidity from other chains to flow into their protocols.
A wrapped token is a representation of an asset from one blockchain that's been made compatible with another blockchain. It's backed 1:1 by the original asset, which is locked up somewhere, and the wrapped version follows the token standard of its new home chain (like ERC-20 on Ethereum or SPL on Solana).
WBTC: Bitcoin on Ethereum
Wrapped Bitcoin (WBTC) is the most well-known wrapped token. Here's how it works:
- You send real BTC to a custodian; historically BitGo, though the custody model has evolved and become more controversial.
- The custodian locks your BTC and mints an equivalent amount of WBTC (an ERC-20 token on Ethereum).
- You can now use WBTC in any Ethereum DeFi protocol; lend it on Aave, provide liquidity on Uniswap, or use it as collateral on Maker.
- When you want your BTC back, you burn the WBTC and the custodian releases your original Bitcoin.
At its peak, over 150,000 BTC (billions of dollars) were wrapped as WBTC. It became the primary way Bitcoin holders participated in DeFi. But the model has a fundamental weakness: you're trusting a custodian. If the custodian mismanages the reserves, gets hacked, or goes out of business, your WBTC could become worthless.
In 2024, BitGo's decision to share WBTC custody with Justin Sun's entities sparked a controversy that led major DeFi protocols to reconsider their WBTC exposure. This episode highlighted exactly why custodian risk matters.