Thea: A Better Decentralized Token Bridge

Thea, Polkadex’s revolutionary interoperability layer, is almost here. Get ready for an easier, safer, and more decentralized token bridge.

6 min readMar 30, 2022


As of right now, when it comes to liquidity in decentralized finance, Ethereum is king. Liquidity can make or break any financial product and the main reason products outside of the Ethereum ‘island’ have failed is that bridging liquidity from Ethereum is either too expensive, too complicated, or too slow for average users. Not to mention token bridges continue to be targeted by hackers, with the “largest exploit in DeFi history” coming to light just yesterday.

Too expensive, too complicated, too slow, not safe enough… sound familiar?

It’s not just liquidity bridges that are plagued by these issues, but the whole DeFi space. With interoperability in mind, Polkadex was born with the purpose of creating solutions to the problems affecting decentralized exchanges. But we didn’t stop there. At Polkadex, we’ve also been hard at work on a solution to the huge user experience problem created by inefficient and insecure token bridges. We’ve called it Thea, and we’re finally ready to talk a little bit more about why we are so excited about it.

Thea’s foundational pillars

In order to redesign the token bridge model, we started from scratch and placed an emphasis on user experience. These foundational pillars guided us through the development on Thea:

  • Thea must allow transfers from any generic wallet
  • Thea must ensure that bridging transactions costs the same as regular on-chain transfers
  • Thea transactions should not take a long time to process
  • Thea transactions should happen in just one operation. No more approve & transfer.
  • Thea users should not need to understand the underlying mechanism in order to use it

A whole new token bridge model

We’re excited about Thea because it is an exponential leap in user experience when it comes to token bridges. In fact, as far as a Polkadex user is concerned, they will not be able to distinguish between Thea Bridge and a centralized exchange’s deposit/withdrawal page.

This is yet another chapter in our Best of both DEXs and CEXs into one revolutionary DEX story. To reiterate, thanks to Thea, the deposit and withdrawal page on Polkadex will feel exactly like its counterparts on CEXs, except it will be fully decentralized.

How does it actually work?

Using Thea to bridge from Ethereum (the first chain to be supported by Thea) will be as simple as sending ERC-20 tokens to the Thea smart contract. It won’t cost you any more than a regular balance transfer transaction. After 25 confirmations on Ethereum, your bridged funds will automatically be in your Polkadex account.

‘Withdrawals’ from Polkadex to Ethereum using Thea will work in a similar way. You will send a withdrawal transaction by entering your Ethereum address and soon you should have your traded assets in your Ethereum wallet. Simple as that.

The whole process will cost you a fraction of what you are currently paying in bridging fees.

Thea? A technical breakdown of the name

Thea is named after Threshold ECDSA (Elliptic Curve Digital Signature Algorithm), the technology that makes a decentralized token bridge between Ethereum and Polkadex possible. More specifically, Thea is a unique combination of Threshold Signature Scheme (TSS), a distributed key generation and signing cryptographic primitive, and light clients, software that connects to full nodes to allow interaction with the blockchain without storing the actual blockchain.


Since TSS has not yet been implemented at a large, production-level public network with a size of more than 10 validators with periodic key rotation, half of the challenge lay in adapting this system to a growing network of at least 140 validators. Technically, Thea is the first application of these technologies at a larger scale.

Light clients

While the threshold signature technology allows for decentralized ownership of the funds moving in and out of Polkadex through Thea, one challenge remains: Verifying transactions from the blockchain we are trying to bridge to and from. We opted to go with light clients as they allow Thea validators to prove the authenticity of information on the layer 1 chain without knowing it beforehand. Essentially, light client technology allows Thea validators to connect to full nodes and interact with the layer 1 blockchain without having to store the entire chain, run a node 24/7, or read and write data on the chain. They’re called light for a reason!

Thea vs the rest

Overall, as opposed to current token bridges with centralized relayers, Thea is run by existing Polkadex validators who act as a decentralized group of relayers thanks to multi-party ECDSA technology. Therefore, Thea bridges have no central point of attack as they are as decentralized as the Polkadex network itself. Unlike existing decentralized bridges based on on-chain multi-sig implementations, Thea is safer, cheaper-to-use and yields a superior performance.

Dive deeper

For those interested in taking a deeper dive into all the intricacies of Thea, Vivek has shared the Thea white paper for all to browse. Let us know your thoughts!

When can we meet Thea? PolkaIDO releases

Very soon! As the interoperability layer of Polkadex, Thea will be fully integrated with Polkadex’s products, which will make it an indispensable tool for Polkadex users. For example, PolkaIDO, Polkadex’s game-changing and democratizing IDO platform, needs the interoperability layer integration in order to bring tokens from other chains and list them for sale in IDOs.

The good news is PolkaIDO is basically complete as it is just awaiting the final go-ahead signal before the floodgates swing open and it is released to the public beta. Once all the feedback from the public testnet is sorted through, PolkaIDO should make its way over to the mainnet.

Overall, Thea should make its way to all of you in public testnet form by next week and mainnet form — with PolkaIDO — soon after that based on the testnet feedback.

The future of Thea

While the Thea protocol is introduced as the underlying technology connecting Polkadex to Ethereum, it will remain as the basis for interoperability between Polkadex and other chains going forward. What this means is that the Thea protocol will be used to create bridges between Polkadex and other chains down the line. On top of that, once Polkadex wins its coveted parachain slot, assets bridged through Thea will also be available to send to other parachains.

Thea and Polkadex

If Polkadex is designed to be a DEX that feels like a CEX, Thea is the underlying decentralized technology that makes ‘deposits’ and ‘withdrawals’ to and from Polkadex feel like they do in a CEX. Thea is designed to be the easiest way to bring liquidity from another chain over to Polkadex — and back — while maintaining control of your funds at all times.

When we started building Polkadex, we knew we were doing something extraordinary. Since then, that mindset has seeped into the fabric of the team. That’s why we throw out the playbook and look for new, better ways to overcome the challenges we encounter along the way. We’re looking to change the game in everything we do. Thea Bridge is just one of the many ways in which we are doing just that.

If Ethereum is the current DeFi liquidity king, it should start making space for Polkadex and Thea. Thea is coming soon with the testnet and mainnet releases of PolkaIDO. Are you ready? Join and follow Polkadex using the channels below to stay in the loop!

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