A cross-chain bridge is a mechanism that allows the same crypto asset to be transferred, or “bridged”, between different blockchains. In fact, Defillama highlights the growing popularity of these bridges — in January 2025, combined net flows across cross-chain bridges reached a record $16.29 billion by volume.
This increase underscores the deeply fragmented nature of the blockchain ecosystem. Specifically, each network largely operates as a closed system, meaning assets on one chain cannot move natively to another. Let’s imagine that you hold USDT on Ethereum as an ERC-20 token or on Tron as a TRC-20 token, yet there’s no direct, on-chain way to transfer it between the two. The reason for this is that Ethereum and Tron maintain separate ledgers that do not communicate with each other.
Cross-chain bridges offer a solution, letting you send tokens directly between blockchains. Let’s explore how these bridges work and how practical they are when it comes to fees and supported chains.
What are the types of cross-chain bridges?
To understand how bridges help blockchains talk to each other, it’s helpful to look at the different ways they actually work. Most bridges today fall into three broad categories: lock-and-mint, lock-and-unlock, and burn-and-mint.
Now, let’s take a closer look at each of them. In a lock-and-mint system, tokens you already hold — let’s say 100 ETH on Ethereum (Company A) — are locked away in a smart contract on that network. Once that’s done, a new version of those tokens, known as wrapped tokens, is created on the destination chain, like Avalanche (Company B). This wrapped ETH has the same value as your original, but now it can be used in apps and services built on Avalanche. When you’re ready to bring your tokens back, the process reverses: the wrapped version is destroyed, and your original ETH is unlocked.
Lock and unlock bridges skip the wrapping part entirely. These rely on liquidity pools that exist on both blockchains. When you send tokens into the bridge on one side, the protocol simply releases the same amount from the pool on the other side. It’s a bit like walking into a currency exchange booth: you give them dollars and walk away with euros, but instead of a person handling it, smart contracts do everything behind the scenes. No new tokens are created — you’re just getting access to what’s already available.
Then there’s the burn-and-mint model. In this approach, instead of locking your tokens, the bridge destroys them entirely on the source chain. Once burned, the same number of tokens is newly minted on the destination chain. This method is often used when moving assets between Layer 2 networks or sidechains, where keeping track of token supply is especially important.
How do cross-chain bridges work?
If you thought the same coins would go to an address but on a different network, that’s not quite the case. There’s a lot happening in the background to make those transfers happen.
To start bridging, smart contracts, oracles, and consensus are involved in the process, working together step by step:
1. Locking or burning tokens on the original chain
First, you tell the bridge to move your tokens from one blockchain to another. The smart contract on the original blockchain jumps into action. It either locks up your tokens in a secure vault inside the contract or burns them, depending on how the bridge is designed. Think of it like putting your money in a safe that only the blockchain controls — it’s still yours, but it can’t be used until the transfer finishes.
2. Oracles deliver the message
Smart contracts can only see what happens inside their own blockchain, so they can’t directly talk to other chains. That’s where oracles come in — they’re like messengers or middlemen. When the smart contract locks or burns your tokens, the oracle watches this happen and then sends a message to the smart contract on the destination blockchain saying, “Hey, these tokens have been locked/burned on the other side.”
3. Getting consensus — making sure everything checks out
Before the destination blockchain acts on that message, it needs to be sure it’s legit. This is where consensus mechanisms kick in.
- Some bridges rely on a small group of trusted validators (kind of like referees) who check the information and say, “Yep, that’s real.”
- Others use a system where a bunch of participants stake tokens and vote on whether to approve the transfer.
- Sometimes, multiple independent validators need to sign off on the transfer before it’s allowed, adding an extra layer of security.
This step is crucial because it prevents anyone from faking a transfer or messing with the data.
4. Unlocking or minting tokens on the destination chain
Once the transfer is confirmed, the smart contract on the destination chain finishes the job. It either unlocks the tokens that were previously locked there or mints brand new tokens to match the ones you locked on the original chain. Now you can use your tokens on the new blockchain, safe and sound.
A real example. How to transfer 100 USDT from Ethereum to Tron Using a Cross-Chain bridge
Let’s say you’ve got 100 USDT sitting in your MetaMask wallet on Ethereum, but the dApp you want to use only supports TRC-20 USDT on the Tron network.
In our example we will try to do this using Symbiosis, a cross-chain swap protocol that supports Ethereum-to-Tron transfers, including USDT, that’s exactly what we need.
Alright, you start by connecting your MetaMask wallet to Symbiosis and entering the amount — in our case, 100 USDT on Ethereum. Then you paste in your Tron wallet address to receive the funds. Behind the scenes, Symbiosis handles the route automatically. At this point, your USDT is first swapped to USDC on Boba BNB Chain, then bridged and swapped again to USDT on Tron.
The entire process is completed in about 1–2 minutes. According to the quote in the app, for 100 USDT you’d receive 92.20 USDT on Tron — so you lose about $7.80 in total fees, including routing through two stablecoins and networks.
All the fees and conversions are handled upfront — no extra steps or manual bridging involved. This example shows how this is more convenient as you don’t have to create an account, deposit funds, and then transfer them — all those extra steps are skipped.
Top 5 crypto bridges in 2025
So, if you’re thinking about testing out bridges yourself, we’ve put together a list of the top 5 tools for cross-chain transfers in 2025.
Note that cross-chain transfer fees consist of a protocol fee — either a fixed amount or a percentage charged for using the bridge — as well as gas fees, which cover transaction costs on both the source and destination networks.
1. Symbiosis Finance
Symbiosis Finance combines a cross-chain bridge with an automated market maker, making it easy to swap crypto across 39 blockchains — from Ethereum and BNB Chain to Polygon and even Bitcoin. As of the time of writing, the number of transactions processed through the platform was 4.13 million. The protocol automatically finds the best routes to minimize fees and slippage, all within a single user-friendly interface.
Among other products, it also offers cross-chain farming, cross-chain zaps, and veSIS staking.
Key highlights:
- Chains supported: 39
- Fees: Symbiosis Finance does not have a fixed protocol fee. Instead, it relies on a dynamic fee model that depends on the specific route and tokens involved in the transaction.The platform aggregates liquidity from various decentralized exchanges (DEXs) and applies the best available rate at the time of the swap.
- Standout feature: Supports 430+ token pairs, integrated swap + bridge in one UI
- Bridge type: Lock-and-unlock
2. Synapse Protocol
Synapse Protocol focuses on low-cost transfers across 20+ blockchains, using liquidity pools and efficient routing. As of the time of writing, we checked the estimated time for bridging USDT from Ethereum to BNB Chain, and the average time was 7 minutes via SynapseBridge.
Key highlights:
- Chains supported: 20+
- Fees: The Synapse bridge charges a default bridge fee of 0.05%.
- Standout feature: Industry-low fees, up to 80% cheaper than rivals
- Bridge type: Lock-and-mint
3. Stargate (LayerZero)
Built on LayerZero, Stargate looks very user-friendly and concise, making it suitable for beginners. Besides the bridge, a user can provide liquidity to the Stargate protocol to earn rewards such as STG or other tokens, or stake. It works with 76 blockchains, including Ethereum, Tron, Polygon, and Optimism.
Key highlights:
- Chains supported: 76
- Fees: Stargate charges a fixed fee of 0.06% for each non-STG transfer.
- Standout feature: Native token transfers with instant finality
- Bridge type: Lock-and-unlock
4. Portal (Wormhole)
Probably the simplest platform for users in terms of design. Portal, powered by Wormhole, supports 22 chains including Ethereum, Solana, Avalanche, Sui, Polygon, and others. It uses a lock-and-mint model: assets are locked on the source chain, and wrapped tokens are minted on the destination chain. The downside is that it doesn’t support many networks.
Key highlights:
- Chains supported: 22
- Standout feature: Supports NFTs and cross-chain dApp interactions
- Fees: 0.01% relayer fee
- Bridge type: Lock-and-mint
5. THORChain (via THORSwap)
THORChain offers a truly decentralized way to swap native assets like Bitcoin, Ethereum, and BNB without wrapping, using liquidity pools of the actual tokens. Supporting 16 blockchains including Cosmos and Solana. Its open-source protocol is secured by a decentralized validator network.
Key highlights:
- Chains supported: 10
- Standout feature: True native asset swaps without wrapping
- Fees: THORChain charges a fixed outbound fee equal to the gas spent (1:1), with a minimum fee of $1.00.
- Bridge type: Burn-and-mint
Overview of top 5 Cross-Chain Bridges in 2025
| Name | Bridge Type | Supported Chains | Additional Features | Fees |
| Symbiosis Finance | Lock-and-unlock | 39 | Farming, zaps, veSIS staking, 430+ pairs | No fixed fee — dynamic |
| Synapse Protocol | Lock-and-mint | 20+ | Industry-low fees | Default fee of 0.05% |
| Stargate (LayerZero) | Lock-and-unlock | 76 | Liquidity rewards, staking | 0.06% for non-STG transfer |
| Portal (Wormhole) | Lock-and-mint | 22 | NFT & cross-chain dApps support | 0.01% relayer fee |
| THORChain (via THORSwap) | Burn-and-mint | 10 | Native swaps without wrapping | 1:1 gas spent, or $1 |
Conclusion and Key Takeaways
Finally, cross-chain bridges are essential tools that solve the problem of isolated blockchain networks — a record $16.29 billion in volume in January 2025, proves it.
As adoption grows, these bridges will become more user-friendly and efficient. Our comparison table shows plenty of strong options, but ultimately, the user decides, whether he needs specific blockchain compatibility or a super user-friendly interface, especially if they are just starting their DeFi journey. In any case, no matter which bridge you choose, always consider the fees involved and take the time to understand how it works before making significant moves.
FAQ
How do I transfer USDT from Ethereum to Tron?
A1: You can use a cross-chain bridge like Symbiosis. Just connect your Ethereum wallet, enter the amount of USDT, and provide your Tron wallet address — the bridge will handle the transfer automatically, swapping and routing as needed.
What’s the best cross-chain bridge to use?
A2: It depends on your priorities. Symbiosis is great for many token pairs and user-friendly transfers, while Synapse offers low fees and Stargate supports many blockchains. Always compare fees and features before making a choice!