Why Bridges Need Gas on Both Chains

A bridge transfer may need ETH on both chains because sending the deposit and using the funds after arrival are separate transactions, each with its own gas cost. The bridge moves an asset or message between networks; it does not make one chain’s ETH pay for computation on another.

Why can’t source-chain ETH pay both gas fees?

Each blockchain records and processes its own transactions, so gas on Ethereum Mainnet is paid to validators there, while gas on a destination network goes to that network’s block producers or validators. The bridge’s message can trigger the destination action, but the destination still needs a way to account for that work.

For a fuller explanation of route selection and what happens on each side, see this Manta bridge route walkthrough. The key detail is that a transfer involves two networks with separate balances and fee rules.

• On the source: You may need ETH to submit the deposit transaction.
• On the destination: You may need the network’s gas token to swap, send or use the bridged asset.
• On the return trip: You need the destination’s gas token to start a withdrawal; completing it may also involve another transaction on the source chain.

Does every bridge require ETH on both sides?

No. ETH is required only when the relevant chain uses ETH for gas and the bridge flow makes you pay that fee. Some networks use another native token, and some bridges or relayers cover a destination transaction’s gas or deduct a fee from the transfer.

There is also a difference between bridging ETH and holding ETH for gas. If you deposit ETH to a network where ETH is the native gas token, the arriving funds may cover later transactions. But if you bridge a different token, or use a route that reserves or deducts fees, you may arrive without enough gas to move it.

A bridge can also send a token that represents ETH rather than the network’s native ETH. The two may have similar market value but are different assets in the chain’s accounting. Check the asset name and destination network before assuming a token can pay gas.

What should you check before bridging?

Check the full route and the destination’s gas token before confirming. The amount shown as “received” can differ from the amount available to use if the bridge takes a fee, accounts for gas, or delivers a wrapped token.

For most users, the practical choice is to leave a small balance of the destination chain’s native gas token after the transfer. That gives you room to approve a token, make a swap or send funds onward; the amount depends on the network and transaction, so check the quoted fee in the bridge interface.

Confirm the source and destination networks, token contract and final amount. A “Manta bridge” search can bring up route pages, but the route name alone does not establish which asset arrives or who pays destination gas. The useful rule is simple: budget separately for the transaction that starts the transfer and the transaction that uses the funds after arrival.