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What Is a Polygon Bridge and How Does It Work?

2022-10-26 12:34:53

Polygon bridge is a cross-chain bridge developed to connect the Polygon blockchain to other blockchains. The polygon bridge allows cryptocurrency assets to be transferred from the polygon network to other blockchains. Polygon bridging occurs via compatible cryptocurrency wallets and a few decentralized exchanges. You might be new to Polygon, what is Polygon? Polygon is a layer-2 blockchain built on the Ethereum blockchain and it’s designed to develop Ethereum-based blockchain networks and scaling solutions. Blockchains have always had problems with interoperability because different blockchains use different protocols and are not flexible enough to communicate with one another and allow the transfer of cryptocurrency tokens across blockchains. In order to address this issue, the Polygon bridge was created.

Bridging Polygon Blockchain to Ethereum

Polygon Bridge - CoinEx

Polygon Bridge was created to introduce a cross-chain bridge with Plasma and Proof-of-Stake security, bringing a trustless two-way transaction channel between Polygon and Ethereum. This bridge allows users to send cryptocurrency tokens from the Polygon blockchain to the Ethereum blockchain and vice versa without taking any risks with third parties or being constrained by market liquidity. Polygon bridge offers a scaling solution that is very fast, has low fees, and is flexible. Polygon was created using a dual consensus framework and uses both Proof-of-Stake (PoS) and Plasma to maximize speed and provide decentralization. Polygon developed the system to support "Ethereum Virtual Machine " sidechains, which allow for arbitrary state transitions. It is essential to know when your cryptocurrency tokens are bridged, the circulating transfer remains unchanged. When a cryptocurrency on the Polygon blockchain is bridged to the Ethereum blockchain, the tokens that leave the Polygon are locked, and the equivalent locked tokens are minted in a 1:1 ratio as a pegged token on the Ethereum blockchain network. To return tokens to the Polygon, the tokens are burnt on the Ethereum blockchain and unlocked on the Polygon. You can read more on Bridging the Polygon network to Ethereum on Polygon documentation.

Proof-of-Stake (PoS) Bridge

There are two bridges built on the Polygon blockchain that can be used to transfer cryptocurrency tokens and assets between Ethereum and Polygon blockchains. The bridges are the Plasma bridge and the Proof-of-Stake (PoS) bridge. The Plasma bridge is more secure compared to the Proof-of-Stake (PoS) bridge due to the Plasma Exit Mechanism. When a user wants to bridge a cryptocurrency token across Polygon to Ethereum, the user has to deposit the tokens via the decentralized bridging platform. The user has to interact with a contract that will lock the amount of cryptocurrency tokens deposited. Once this approval transaction has been confirmed, the owner of the asset token interacts with another contract called the RootChainManager contract to complete the deposit. Withdrawing assets through the Proof-of-Stake bridge is lightning fast. It's as simple as burning the cryptocurrency tokens on the Polygon chain, collecting the transaction hash, and submitting it to the RootChainManager contract. The RootChainManager then invokes a contract to free the funds locked on the Ethereum chain. Once the burn transaction has been verified on the Polygon chain, it takes an average of about 30 minutes to 3 hours to be checkpointed. Checkpointing is the process of integrating Polygon transactions into the Ethereum blockchain. After checkpointing, the proof of this burn transaction (transaction hash) is submitted to the RootChainManager, triggering a contract to release the locked cryptocurrency tokens that were deposited. All these processes are automated and fast, a user bridging doesn’t witness all these processes when interacting with the Polygon bridge. 

Polygon Plasma Bridge

The plasma bridge provides greater security than the Proof-of-Stake (PoS) bridge due to the Plasma exit mechanism. One drawback of the Plasma bridge is its restrictions; a 7-day withdrawal period applies to all withdrawals from Polygon to Ethereum made using the Plasma bridge. A user must deposit cryptocurrency tokens via a Polygon contract on the Mainchain in order to communicate with the Plasma bridge. The corresponding cryptocurrency tokens will be minted on the Polygon chain once the deposited tokens are confirmed on the mainchain. The remaining tokens on the Mainchain can be withdrawn by the user whenever they are ready. The cryptocurrency token withdrawals are initiated from the Plasma Sidechain. The Polygon block layer's blocks are validated since the previous checkpoint at intervals of 5 minutes. A token called Exit NFT is created with an equivalent value once the checkpoint is submitted to the mainchain Ethereum contract. A process-exit procedure can be used to claim the withdrawn funds back to your Ethereum account from the mainchain contract.

Polygon PoS Bridge vs Plasma Bridge

Polygon PoS Bridge vs Plasma Bridge

Configuring your Metamask to Polygon Network

MetaMask is a popular non-custodial Ethereum wallet that connects easily to different blockchain networks. But you have to configure your Metamask to support some blockchain networks. Below are the steps to set up your Metamask blockchain app to connect to the Polygon network. 

Step One

Download the Metamask extension for your PC if you use a PC, or the Metamask app for your mobile phone if you use a mobile phone. Then set up your Metamask wallet and ensure to keep your private key or seed phrase safe.

Step Two

Log in to your Metamask app, click the navbar and go to settings, after opening “settings”, select Network and select “Add Network”. If you are accessing your Metamask via your PC extension, the Ethereum network is the default network of Metamask, at the top click Ethereum Mainnet, scroll down and select “Add Network”. If Polygon Network is on the drop-down list, select it. But if Polygon isn’t there, go ahead with the steps below.

Add Polygon Network to Metamask

Step Three

After clicking “Add Network” Input Polygon network parameters as follows:

Network Name: Polygon Mainnet

New RPC URL: https://polygon-rpc.com/

Chain ID: 137

Symbol: MATIC

Explorer: https://polygonscan.com

Input Polygon network parameters


Interoperability was a problem for decentralized exchanges because tokens couldn't be sent from one blockchain to another. Polygon Bridge was developed to address this interoperability problem and increase the flexibility of blockchains. Polygon developed two bridges, the plasma and the proof-of-stake (PoS), and they both have their pros and cons.

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