Lock-and-Mint vs Burn-and-Mint

The dominant bridge pattern locks real collateral on the origin chain and mints a wrapped token on the destination — wETH on Arbitrum backed by ETH locked on Ethereum, for example. Supply on the destination is only sound if every wrapped unit maps to locked or burned collateral somewhere.

Some bridges burn on both sides when native assets exist on multiple chains — USDC Circle CCTP burns on source and mints natively on destination rather than maintaining a permanent lock pool. The accounting differs, but the invariant is the same: no unbacked mints.

Liquidity fragmentation is the user-facing cost. Wrapped ETH on Arbitrum, Optimism, and Polygon are different tokens with different contract addresses. DeFi composability on each chain depends on which bridge path created the supply you hold.