Avail, a project spun out of Polygon earlier this year to handle data storage and verification for blockchains, launched its “data attestation bridge” on Friday, a new offering designed to reduce costs for layer 2 and layer 3 chains in the Ethereum ecosystem.

The data attestation bridge helps secure data off-chain. It’s connected to Ethereum, and can be used by both zero-knowledge and optimistic rollups that use Ethereum as a base layer.

Storing data on Ethereum can be expensive, so Avail aims to be a solution for layer 2s and 3s to publish data off-chain, to reduce the high transaction fees that often come from posting data on the main Ethereum blockchain. The idea is to spare the main Ethereum blockchain from getting congested with anything besides execution and settlement activities.

The challenge of handling the data and setting up separate networks for data storage is known as the ”data availability problem,” or DA – an arena that includes developing cryptographic systems to prove that the data exists (i.e. that it’s available) and that it’s right.

“The data attestation bridge establishes a direct connection between the L2 rollup’s data and the L1 via Avail’s off-chain data availability layer,” Avail said in a press release.

The bridge is one component of what Avail will offer in the layer 2 ecosystem. In the longer term, Avail wants rollups to launch entirely on top of its network. These networks could include so-called validiums, which are Ethereum scaling solutions that store transaction data off-chain.

“When an L3 or a validium sends the transaction data to Avail, the data attestation bridge provides the attestation on Ethereum,” Anurag Arjun, the founder of Avail, told CoinDesk. This then proves to Ethereum that “whatever data was submitted by the rollup to Avail is actually available.”

In March, Avail spun out of Polygon, where Arjun had been a co-founder. In June, Avail released the second phase of its “Kate” testnet, where it went through a series of tests to encourage validator participation in the network.

Read more: Polygon Spinoff Avail Network Starts Phase 2 of Its Testnet