Polygon bridge deposits and withdrawals require signing access, a supported asset, and gas on the network executing each transaction. For example, a Polygon bridge withdrawal starts with POL on Polygon and finishes with ETH on Ethereum because each network charges for its own operation. These requirements assume you pay your own gas unless sponsorship is explicitly shown.
Polygon bridge resources by signed stage
Each wallet prompt needs resources on the network named in that prompt. The asset you are moving and the asset that pays gas are separate balances. A useful map is:
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Ethereum approval: If a token allowance is needed before a deposit, the account holding the token signs an Ethereum transaction and pays its gas in ETH. An existing sufficient allowance may remove this stage.
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Ethereum deposit: The account supplies the supported asset to the bridge contract and pays Ethereum gas in ETH. The deposit transaction does not spend POL from Polygon.
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Polygon transaction: An app transaction after a deposit, or a withdrawal that starts on Polygon, needs signing access and POL for Polygon gas.
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Ethereum exit: A standard mapped-token withdrawal needs a later Ethereum transaction to claim the asset. Whoever must submit that exit needs access to the responsible account and ETH for its gas.
This map explains why a single gas balance rarely covers the whole journey. ETH held on Ethereum cannot pay a Polygon transaction, and POL held on Polygon cannot pay an Ethereum exit. Gas is charged for the operation being executed, independently of whether that operation moves ETH, a stablecoin, or an NFT.
Depositing from Ethereum to Polygon
A bridge to Polygon begins with an Ethereum transaction, so the depositing wallet needs ETH as well as the asset it will transfer. For an ERC-20 token, the bridge may first request an approval: a transaction that permits a specified spender contract to use up to a stated token amount. The approval and the deposit each consume Ethereum gas if both are needed.
The allowance belongs to a particular token, owner account, and spender. Holding enough of the token does not establish that the intended bridge contract has permission to move it. Conversely, a sufficient existing allowance can let the deposit proceed without another approval. For an NFT, the wallet may show approval for one token ID or operator access to a collection; that permission deserves the same attention as an ERC-20 spending limit.
The deposit must also use a supported asset mapping between its Ethereum token and its Polygon representation. For mapped tokens, Ethereum bridge contracts custody the deposited asset while the corresponding token is made available on Polygon through the bridge’s mapping and deposit handling. A wallet balance alone says nothing about that mapping. Asset type matters too: an ETH deposit and an ERC-20 or NFT deposit need not present identical contract calls or approval prompts.
Once the asset arrives, a planned app transaction on Polygon is a new operation with its own gas requirement. A user might bridge ETH or a stablecoin successfully, then find that the first Polygon transaction cannot be submitted. The reason is that the received asset does not automatically become POL. Polygon’s native gas token is POL, as described in the Polygon documentation on POL; the wallet needs a usable POL balance for ordinary self-funded transactions there.
Withdrawing mapped tokens to Ethereum
A Polygon bridge withdrawal of a standard mapped token has two signed stages on different networks. The Polygon transaction initiates the withdrawal, commonly by burning the Polygon-side representation of the asset. That transaction needs the token in the initiating account, access to its signer, and POL for gas. It does not itself release the Ethereum-side asset to the wallet.
After the withdrawal is included in the bridge’s checkpoint process, an exit transaction on Ethereum uses proof of the Polygon withdrawal to release the corresponding asset. The exit is another onchain operation, paid for in ETH. Its gas must be available before the release completes: even if the asset being claimed is ETH, the pending claim cannot be treated as an existing ETH gas balance.
This is the point at which account access matters beyond the first signature. If a hardware wallet, smart account, or other controlled account starts the withdrawal, establish how the later Ethereum exit will be signed for that transfer. Leaving POL in the wallet after the Polygon transaction does not solve a missing Ethereum signer or ETH balance. The exact completion arrangement depends on the withdrawal flow and account used.
What a wallet prompt tells you
A Polygon PoS bridge transfer is ready only when the prompt’s network, purpose, and funding match the intended stage. On Ethereum, an approval prompt names a token and spender and changes an allowance; a deposit prompt sends the asset into the bridge flow. On Polygon, a withdrawal prompt starts the return of the mapped asset. The later Ethereum exit completes that return.
Read the displayed network and gas asset alongside the transaction purpose. A prompt asking for POL points to a Polygon operation; one asking for ETH gas points to Ethereum. For an approval, inspect the spender and allowance amount because the signature grants token access, rather than completing the deposit. For the exit, identify which account is expected to submit the claim and whether that account can pay Ethereum gas.
A visible token balance therefore proves only that the wallet holds an asset on one network. Readiness also depends on supported mapping, any required allowance, native gas at every signed stage, and access to the account that must finish the withdrawal. An interface may explicitly sponsor gas or bundle funding with another operation; rely on that only when the transaction terms actually show it. Otherwise, prepare ETH for Ethereum operations and POL for Polygon operations before starting.