Polygon: L2 or not L2?

The tech behind Polygon

Polygon’s PoS “main chain”


  • A user deposits funds into the bridge in the source (or parent) chain, and a representation of the assets is issued in the destination (or child) chain.
  • The bridge is notified about the new account balances and enables the withdrawal process.
  • From here on, the user can withdraw their assets in the child chain. The assets in the parent chain are burnt and the user’s balance in the child chain is updated.
  • A PoS bridge, which is faster and more flexible, but a less secure solution than the second bridge currently supported by Polygon, the Plasma Bridge. In the PoS bridge developers need to map the addresses of the source and destination contracts, block the assets, and run the exchange. The PoS bridge uses Matic’s state sync mechanism, which is the scheme used by the Metis POS chain to read from Ethereum. These exchanges take 10 to 30 minutes.
  • The Plasma bridge provides increased security guarantees but with a 7-day withdrawal period associated with all withdrawals from Matic to Ethereum. In the next figure you can get a glimpse of how the Plasma bridge operates for the case of an NFT migration. You can follow this link for further details.

Polygon SDK

  • The blockchain layer is the core of the SDK. It implements everything related to block and the state of the chain. It manages the logic that happens when a new block is included into the blockchain, and defines the state behavior. The state represents the state transition object. It deals with the state changes when a new block is added to the chain and the state handles (the execution of transactions), executing the EVM, and changing the state Merkle Tries of the blockchain according to the transaction being performed.
  • The consensus layer provides an interface for different consensus algorithms. It lets you plug in or implement any consensus algorithm you want into your blockchain. The only consensus currently supported by the Polygon SDK is the Istanbul Byzantine Fault Tolerant (IBFT). But according to Polygon’s documentation, the company is also working on implementations for Clique, Ethash, and PoW.
  • The TxPool module is what you would expect: it represents the transaction pool implementation, where transactions are added from different parts of the system, for their subsequent processing by the consensus and the blockchain layer.
  • Finally, the SDK includes a p2p networking layer for the communications between peers implemented over libp2p, and a gRPC and JSON RPC APIs to interact with the peer.

What is yet to come

  1. Polygon chains: Polygon is planning to support two major types of Ethereum-compatible networks: standalone networks and networks that leverage “security as a service”.
  • Standalone chains are fully independent blockchain networks in charge of their own security. They enjoy full independence, but the level of security of the chain depends on the number of nodes participating in the network, and the specific consensus being used. This can be a great fit for big enterprises or established projects and communities.
  • On the other hand, secured chains are blockchain networks that use Polygon’s security layer instead of establishing their own independent validator tool like standalone chains. This security as a service can come in the form of a delegated pool of validators, or the combination of other verification schemes like rollups and fraud proofs.

How does Polygon differ from a L2 solution?

  • While Metis has a clear proposal to tackle Ethereum’s scalability limitations, a user of Polygon needs to navigate through all of its solutions to understand the one that suits its needs: the Matic PoS chain to overcome Ethereum’s scalability limitations, bridges if interoperability of networks is the key issue, or the Polygon SDK to build a brand new EVM-compatible standalone chain.
  • Matic PoS Chain’s checkpoint scheme is quite similar to an optimistic rollup. But if you then look at Polygon’s roadmap, the company is also thinking about implementing optimistic rollups. So how can this be? My take is that Polygon’s rollup implementation will belong to the pluggable security layer. Metis and other L2 solutions on the other hand already come with optimistic rollups “by design” as part of their protocol; it is not an optional layer that needs to be configured ad hoc into your chain. The chain just has it. I was trying to find some numbers on the performance of the Matic PoS chain in order to compare them with the numbers we saw in this comparison between Metis and other optimistic rollup solutions, but couldn’t find anything. However, at a glance, Metis’ sequencing pool, and the use of rangers as verifiers with a stake in the network, seem more robust than the ones in place for the Matic PoS chain. Matic’s PoS chain more closely resembles the optimistic rollup approach from projects like Arbitrium.
  • Companies looking to deploy blockchain applications may choose Polygon to deploy their standalone chains. This may make sense for certain use cases, as many L2 solutions are not focused on corporate use cases, and they lack the isolation and security guarantees required by this kind of organization. However, this won’t be the case for solutions like Metis. Metis supports DACs (Decentralized Autonomous Companies) from scratch, which gives organizations access rights and other permissioning schemes without requiring the deployment and maintenance of a complete independent chain (with the overhead and the burden that this may entail).
  • Polygon standalone chains can also be a great way of horizontally scaling use cases. However, L2 solutions like Metis also allow this horizontal scale by decoupling the state and the execution of transactions without requiring the deployment of a brand new chain.
  • When I was reading about Polygon’s security layer and “validators as a service,” it also reminded me about how Metis already has “by default” rangers and sequencers with a stake securing the L2 and committing blocks to the mainnet. However, while in Polygon’s security layer, validators are “rented” for specific standalone networks. With Metis, rangers and sequencers rotate through every DAC enforcing that everything is working as it is supposed to in all of them (not only a small number of selected ones).
  • Something that many L2 solutions lack and where Polygon excels is in the interoperability between chains. I would be curious to see how Polygon bridges operate with L2 solutions like Metis. Metis, like almost every L2 solution, is EVM-compatible, which means that it would be theoretically possible to use Polygon bridges to perform token exchanges between Metis and other Polygon-compatible chains. Can you imagine how powerful a decentralized application would be by leveraging Metis Layer 2 capabilities (with its IPFS integration), and Polygon interoperability features?
  • Finally, let’s come back to something I briefly brought up at the beginning of the article: the security and trust guarantees of Polygon bridges and its interaction with L1 are weaker than those of L2 solutions based on rollups like Metis. This is no small item. We’ve seen many times how so-so security has led to disastrous results for blockchain projects. Since Metis is a fully decentralized platform running on top of the secure Ethereum network, it’s a more secure option than a centralized commit-chain like Polygon.

It all boils down to who you choose to trust

Closing words



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