Proposal to open-source the Cardano-to-Polygon NFT bridge developed by Clay Nation and The Sandbox

💡 SIP: Ideas All Ideas
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GM Sandfam,

I’m excited to share an idea that could make a big difference for the Sandbox ecosystem and the way it connects with others.

As part of Clay Nation’s collaboration with The Sandbox, together we created the first-ever NFT bridge between Cardano and Polygon—and it’s working great! Now, I’m thinking: why not open-source it?

Some context

The Clay Nation and Sandbox Teams collaborated to achieve the launch of the very first Cardano to Polygon NFT bridge. The bridge functions as an on-chain registry, verifying NFT ownership on Cardano and transforming 2D NFTs into 3D voxel assets compatible with The Sandbox. Once transformed, these assets are registered on the Polygon blockchain to ensure interoperability. This process represents a new approach to cross-chain NFT utility, enabling Cardano NFT holders (in this case, Clay Nation NFT holders) to access their assets in The Sandbox.

With this setup, we’ve opened-up cross-chain utility between Cardano and Polygon. Now that we’ve seen how well it works, it feels like the perfect time to share the tech and invite others to help it grow.

What we’re proposing

  1. Open-Sourcing
  • We’ll release the code under an open-source license.
  • Include clear docs, architecture details, and tips for contributing.
  1. Support & sustainability
  • The Clay Nation team will help get the open-source project started.
  • I’m suggesting that Sandbox DAO allocate resources to ensure it thrives long-term.

Benefits for The Sandbox Community

  1. Devs from both Cardano and Polygon can use and improve the bridge.
  2. Attracts new talent and projects to the ecosystem.
  3. Positions The Sandbox as a leader in blockchain interoperability.

Fundamentally, we believe that cross-chain collaboration can only make The Sandbox stronger and more versatile. Opening-sourcing the code for the bridge will speed up adoption and improvements by bringing more people to the table, as well as helping us develop better security and transparency in the process.

Any feedback is welcome; your thoughts will be valuable to us in refining our formal proposal, which I plan to draft in the coming week.

Kindly :sun_with_face:

Lenna Onto

Founder | Clay Nation

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Good day,

I would appreciate it if you could answer the following questions to aid my understanding.

  • How would this initiative affect user engagement and retention within The Sandbox ecosystem?
  • What technological trends in blockchain and NFTs make this the right time for such an initiative?

Thanks for taking the time.

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This is a really unique proposal. It sounds like the sort of thing that would unlock A LOT of potential.

I’m struggling to understand all the implications for TSB

Once transformed, these assets are registered on the Polygon blockchain to ensure interoperability

As in I can own a Rabbids avatar or sword on Cardano chain and it would show up in my avatar inventory in-game to play as and equip? Is it as simple as that, or does there have to be some enabling thing that authorizes only specific NFTs to be usable in-game?

Please explain in as simple language as you can, for my sake! :slight_smile:

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Hello,
Interesting topic.
Just curious about why cardano.
Based on this chart it doesn’t look like the more used blockchain.
Tbh, I’m really not fan of base and even less of solana but it looks more relevant to go in this direction. ( this graph should be taken with caution knowing that many users on sol are probably bots.)
If you ask me, I’ll suggest BNB chain (just personnal feeling) to do that.

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Hey Lena,

Thank you for your ideas and very interesting. I am from the opinion that the interoperability between network is another step that will ease the access to web3 for the public. Nowsadays; this complexity is slowing down the adoption and requires a lot of time for new joiners to understand. Giving the possibility to use within TSB other NFTs can only be beneficial.
With regards to what you have done on the clay nation exp within TSB can you explain maybe what was achieved. eg showing the NFT from 2d to 3d transformation.
What kind of limitation are existing for this transrformation?

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I hadn’t considered it’s usage…that’s a really interesting graphic Sebga.

I’m hesitant on BNB. It has applied really heavy restrictions to US users, understandably so given the regulatory environment, but still, it means that people like me will find it difficult to participate…versus a more permissionless chain like Polygon, Solana…Ethereum even.

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Hey, @lentilonto :wave:t4:
It seems your idea is getting a bit of attention here :rocket:

You’ve got some questions from the community outlined above

This is a really cool suggestion for a SIP and I’m excited to see what the community, the delegates, and your team can do to bring this to a vote.

We’ll be doing a SIP Training in a couple of weeks, but this was fleshed out into a solid proposal, it may get good traction.

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Hi Hishmad,

Apologies for my delayed response over the festive period :christmas_tree:

Hope my answers help - I really appreciate the questions and starting the discussion.

To answer your first question: How would this initiative affect user engagement and retention within The Sandbox ecosystem?

We strongly believe this could be a game-changer for user engagement and retention. The bridge allows users to bring their favorite NFT from Cardano into The Sandbox and use it in a meaningful way to connect with their community. That’s the kind of personal connection that keeps people coming back.

It’s all about personalisation and accessibility. Users feel more invested when they can bring their existing NFTs to life in The Sandbox. And it’s not just about the Cardano crowd—this kind of innovation attracts developers and creators from other ecosystems, adding more people, more ideas, and more reasons for users to stick around. It also underscores The Sandbox’s leadership in metaverse interoperability.

The fact that users don’t need to transfer NFTs from other chains to Mainnet or Polygon makes The Sandbox much more accessible. It’s an easy first step for new users to get comfortable with both The Sandbox and cross-chain functionality. We’ve seen this first-hand with our community when we introduced them to the Sandfam.

Finally, this bridge will likely inspire projects to build unique experiences alongside their avatars, encouraging creators to engage their communities and bring them into The Sandbox. It’s a win-win for everyone involved.

To answer your second question: What technological trends in blockchain and NFTs make this the right time for such an initiative?

We believe this is the perfect time for an initiative like this because so much is happening in blockchain and NFTs. People now expect their assets to work across platforms, and interoperability is becoming the standard. With more platforms embracing cross-chain capabilities, users value the freedom to use their assets wherever they go.

NFTs are also evolving beyond digital art to become functional, interactive assets. People want to use them in games, metaverses, and other spaces. The metaverse itself is continuing to scale too, and this bridge ties everything together, giving Cardano users—many of whom might be new to metaverses—a way to join in.

For new users, the bridge makes The Sandbox more accessible. It allows them to use assets they already know and love on their preferred blockchain, making the transition smoother and less intimidating.

Finally, open-sourcing this bridge aligns with the growing push for decentralisation.

Thank you so much - let me know if I can add to that :slight_smile:

Lenna

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Hey Lanzer

Great question. Have tried to break it down a bit:

It’s almost that simple, but there’s a bit of backend magic happening. First, the protocol checks your Cardano wallet to confirm you actually own the NFT. Once that’s verified, the bridge communicates this ownership to Polygon, where the NFT is transformed into a 3D voxel version of the original image. This version is then ready to be accessed and used in The Sandbox.

Now, not every NFT can instantly work in-game. Only certain collections (like approved ones) are authorised to keep things balanced and high-quality. To expand this functionality, we’d love to work with The Sandbox to design a simple yet robust application process for interested projects. This process would allow projects to submit their collections for approval, ensuring that they meet the technical and aesthetic standards of The Sandbox while still allowing for creativity and diversity. Such a process could include guidelines for compatibility (e.g., metadata requirements, 3D model support) and offer resources for projects looking to adapt their assets for in-game use.

For you as the user, the process is still pretty straightforward. You link your Cardano wallet to a Polygon wallet using a small dApp (decentralized application). After that, you log in to The Sandbox as usual, and your authorised Cardano assets will automatically appear in your Sandbox inventory, ready to equip and play with.

Thanks!

Lenna

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Hey @sebga and @Lanzer

That’s a totally valid question and one we should think about.

While Cardano might have the biggest active user base by numbers, it has some unique strengths that make it a great fit for this kind of initiative.

First, from our experience operating in the Cardano ecosystem for over four years, we’ve seen how community-driven it is. The people in the Cardano space are incredibly passionate and engaged, which makes collaboration much easier and more meaningful. This kind of dedicated audience is a big plus for any cross-chain project.

Second, Cardano is one of the most eco-friendly blockchains out there, thanks to its proof-of-stake consensus model. This aligns really well with The Sandbox’s long-term vision of building a sustainable metaverse.

Third, Cardano offers untapped potential. Unlike Ethereum, Solana, or Base—which are already saturated with projects—Cardano provides an opportunity to explore new territory and bring something fresh to the table. What’s especially exciting is that this bridge has the potential to expand beyond Cardano to include other non-EVM blockchains in the future, making it a foundational step toward broader interoperability.

Lastly, the results we’ve seen so far speak volumes. With the two Clay Nation x Sandbox experiences, we reached impressive numbers, including a standout performance during Alpha Season 4, where one experience ranked #8 with 106,841 players. This shows that there’s already strong interest and engagement when we combine Cardano assets with The Sandbox ecosystem.

Thanks,

Lenna

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Thank you @theKuntaMC

Apologies there was a small delay with our responses over the holidays!

I hope to join the training session and get this fleshed out as suggested.

Lenna

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Hey @KCL

Thanks for this :slight_smile: I’m sorry it took me a while to respond over the holidays.

One of the coolest things we accomplished was taking a collection of 10,000 Clay Nation NFTs and transforming them into 3D voxel models. This meant that instead of just viewing your NFT, you could actually use it in The Sandbox while still securely holding the original NFT in your Cardano wallet. It was really cool to contribute significantly to cross-chain interoperability.

We didn’t stop at just transforming the NFTs; we brought them to life with a new aesthetic and created custom experiences to introduce the Clay community to the fun and creativity of The Sandbox. The response was amazing—our standout experience during Alpha Season 4 ranked in the top 10 experiences, securing the #8 spot with over 100,000 players. Being part of both the Alpha Season 4 and the Music and Love event was a highlight for us and the community.

Of course, there are some challenges. Not all 2D designs translate perfectly to 3D voxel models—it takes some tweaking to ensure the final result looks great and fits The Sandbox’s distinctive style.

Another limitation is that only approved collections can go through this transformation process. While this keeps the ecosystem balanced and high-quality, it means that the process is a bit restricted initially. However, seeing a Clay Nation character running around in The Sandbox and the joy it brought to our community made all the effort worthwhile.

Looking forward to discussing further

Lenna

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Hey Lenna,

Thanks for your answer. I found out this video that is showing the result.

So if I am correct the Clay community could play with their NFT transform in avatar in TSB?
Would you have by chance some numbers of “transformation” that were done during those different events? (eg how many of 100k players used a Claynation NFT…) This would support backing up the “benefit” part of the SIP.

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Thank you for the response! How do you measure which community is the biggest or most active?

Would you mind helping me understand the significance a little bit more? Are we talking Bitcoin?

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Yes, that’s correct. Members of the Clay Nation (genesis collection) community could transform their NFTs into playable avatars in The Sandbox. During the events, they could use these avatars to interact with the experiences we created.
As for numbers, while we don’t currently have precise statistics on how many of the 100k players used Clay Nation NFTs specifically, we can share that there was significant engagement from our community. We will ask The Sandbox is they are able to share the stats on this.
We did things a little differently and required Clay Nation holders to unlock their voxel character. From this process, we do know that over 800 individual avatars were actively upgraded, to be used in the Sandbox.

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When we say this bridge could expand to other non-EVM blockchains, we’re referring to blockchains that don’t natively support Ethereum Virtual Machine (EVM) compatibility but still have significant user bases and unique ecosystems.

While Bitcoin is technically a possibility, the focus could be directed more towards blockchains with strong NFT and gaming ecosystems, such as Alogrand or Tezos for example. By expanding the bridge to include such chains, The Sandbox can attract a broader audiences and solidify its position as an interoperable metaverse.

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That’s amazing!

They could be an incredible addition to the player base in TSB.

Do you know if many were active in TSB before upgrading their Claynosaurs?

What data do you need?

You can shoot me a DM on here with more info if you’d like to!!

I’ll do what I can to help get more info for you.

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What are your thoughts on this SIP Idea? :point_up:t4:

Any feedback/suggestions?? :thinking:

@moefat @mo_ezz14 @rocksymiguel @Biversen @cryptodiplo @Airvey @meowl @Oldwon @sebga

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@lentilonto hello.

What I want to learn.

• First of all, I’m not asking why Cardano network. as far as I understand, you are using Cardano because your project is there. right? Personally, Ether base is the most widely used system and I would choose the AVAX network for such a thing.

• What you are actually doing is simply taking an existing NFT and automatically Voxelizing it and creating it as a new NFT in the Polygon mesh. Is that correct?

• What properties will NFTs converted as voxels contain? For example, if it is Avatar, will it give IDLEs automatically? Or does it just output them as a basic model. Can we decide what kind of Voxel model it will be?

• How good a decision is it to keep the conversion process only for approved collections? How does it help if not everyone can implement and use the NFT they want? Isn’t that something that inhibits community?

• How and according to what will the valuation of 2D - 3D converted NFTs be?

• Wouldn’t it be better if TSB did this in general by itself, as it did in polygon? why do we need a separate tool? Besides Polygon, a Cardano wallet could be registered on the site, so that everything would appear in my TSB account. I can use it to migrate your tool to 3D voxel. so there’s no need for cross-network transfers.

Can you send me the link to your experience?

On what basis did you position yourself 8th in the top 10?
A lot of players have been in and out of AS4 games just to take screenshots and stuff like that. But that doesn’t mean that the experience has been played.

I would like to check the accuracy of the measurement.

Thanks you.

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I had reservations about the merits of this proposal.
Lentilonto responded with relevant arguments but I am still not convinced. Cardanno may have potential but it’s not a blockchain I personally use.
If you offered me some things with Near protocol, for example, I would think about it a little more given the AI ​​aspect of this network, which could potentially bring a real plus in the future.
But Cardano, I’m skeptical.

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