A cross-chain bridge, as its name suggests, is simply a path that connects two separate blockchains. Users can send tokens from one blockchain to another using it. Assets from a separate blockchain, unfortunately, are usually incompatible with the target network. As a workaround, these bridges produce synthetic versions of assets from the source chain on the target network, before locking the original token on the source chain. This process is called wrapping. If you transmit BTC to an Ethereum wallet, for example, the wallet will receive a wrapped version of BTC, an ERC-20 token, which is the Ethereum standard.
Classifying blockchain bridges
Some bridges only allow users to send a token from a source chain to a second chain, but not from the second to the source. Such bridges are called unidirectional or one-way bridges. For instance, one can wrap a Bitcoin into a wrapped Bitcoin. However, one cannot send ETH back to the Bitcoin network via the same bridge. There are other types of bridges that allow users to exchange tokens between two different networks regardless of direction. These are called bidirectional or two-way bridges. A good example of such is Solana’s Wormhole.
Reasons for using blockchain bridges
The utilization of a cross-chain bridge may be required for a variety of reasons. For one thing, you could wish to employ a blockchain that is both cheaper and speedier. This is particularly true for Ethereum users, who are continually beset by high gas fees and sluggish transaction speeds. Furthermore, even if Ethereum users wanted to keep their exposure to their ERC-20 tokens, they could employ layer 2 solutions like Polygon or Arbitrum to achieve quicker speeds at a lower cost.
Other users, on the other hand, may require access to markets hosted on other blockchains. The Orca protocol, for example, is only available on Solana, but it supports a wrapped version of ETH. That being said, let’s look at the top bridges available for Ethereum users to access other popular networks.
Ethereum to Binance
Launched in 2020, the Binance Smart Chain is a smart contract-enabled blockchain that also boasts Ethereum Virtual Machine (EVM) compatibility. It is home to a wide range of popular applications spanning gaming, DeFi, and metaverse projects, just to name a few. Ethereum users looking to access this popular chain can do so using the Binance Bridge. This bridge allows Ethereum users to wrap their ERC-20 tokens into BEP-20 assets, which can then be used on popular BSC platforms like PancakeSwap. The MetaMask wallet can be used to gain access to this bridge.
Ethereum to Avalanche
The Avalanche chain is one of Ethereum’s main competitors. In addition to its own native dApps, it is EVM compatible and supports a host of Ethereum apps such as Aave, Curve, and Sushiswap. The Avalanche Bridge allows Ethereum users to transfer their ERC-20 tokens to this quicker and lower-cost network. In so doing, the “.e” symbol is applied to the bridged assets. If you bridge USDC to Avalanche, for example, the wrapped currency will be USDC.e.
Notably, in order for a token to be successfully transferred, three of the Avalanche Foundation’s four partners, known as wardens, must approve the transaction. This bridge, however, is incompatible with the ERC-721 token standard. As a result, NFTs cannot be sent to Avalanche.
Ethereum to Solana
Solana is one of the most powerful “Ethereum killers” on the market. It offers faster transaction speeds and lower transaction prices than Avalanche. Every half-second, the network verifies a new transaction block. Bridges like Wormhole and Sollet enable Ethereum users to transfer their tokens to this far more efficient blockchain.
ERC-20 tokens bridged to Solana using Sollet and Wormhole, however, are incompatible since the two bridges produce two different wrapped copies of the tokens. For that reason, Wormhole is the more popular of the two bridges, owing largely to its ability to transfer NFTs in both directions. However, it recently made headlines after an exploit in February 2022 resulted in the theft of $326 million in assets.
Solana also boasts a third cross-chain bridge known as Allbridge. Through Allbridge, users can transfer tokens to Solana from Ethereum, BSC, Avalanche, and a variety of other networks.
Ethereum to Polygon
Polygon is a layer 2 alternative to Ethereum. For that purpose, there are a number of bridges that allow tokens to be transferred between the mainnet and the Polygon sidechain. Since its inception in 2017, the latter has grown at an exponential rate, making it the most popular of Ethereum’s sidechains. Several of Ethereum’s native dApps are now hosted there.
The Polygon POS Bridge is the primary bridge for transferring tokens to Polygon. Between these two chains, this bridge allows ERC-20 tokens to be transferred. Depositing tokens from Ethereum to Polygon takes only a few minutes, whereas withdrawing tokens takes almost an hour.
Plasma is another popular link between these two chains. Plasma is typically used to withdraw ETH to the Ethereum main network. However, these withdrawals can take up to 7 days to take effect.
Ethereum to Terra
Terra is a popular DeFi host blockchain that is built using the Cosmos SDK. Popular applications on this chain include Anchor Protocol and Mirror Finance. This chain has a bi-directional bridge with Ethereum named Shuttle.
By design, the bridge was meant for the unidirectional transfer of Terra-based assets to Ethereum. Due to this, only whitelisted assets can be transferred bilaterally between the two networks. Ethereum users are required to convert their ETH into Terra-based ERC-20 tokens like the wrapped UST. Alternatively, they could stake their ETH on Lido Finance, which would yield them staked ETH (stETH). The stETH can then be bridged to Terra, which entails wrapping it into bETH, which can be used on apps like Anchor Protocol.
In a nutshell
Ethereum, since its inception in 2015, is arguably the most popular destination for dApp developers and consumers on account of having been the first to launch with smart contract capabilities. However, its scalability issues have resulted in network congestion and, as a result, hefty gas fees. To get around these, Ethereum users must continually employ cross-chain bridges to move their assets to faster and cheaper blockchains.