Definition

Rollup

A Layer-2 scaling solution that batches many transactions off-chain and posts a compressed summary back to Ethereum (or another L1).

Rollups solve Ethereum's scaling problem. Instead of every transaction running on L1 (slow, expensive), rollups execute transactions on L2 and post the results to L1 in compressed batches. Users get fast/cheap transactions; L1 still provides settlement security. Tens of thousands of rollup transactions can settle in a single L1 batch.

Two main flavors: Optimistic rollups (Arbitrum, Optimism, Base) post transaction data to L1 and assume it's valid; if anyone disputes, they submit a fraud proof during a 7-day challenge window. ZK rollups (zkSync, StarkNet, Linea, Scroll) post a cryptographic validity proof with each batch — no challenge period, but the proof system is more complex.

Rollups have become Ethereum's scaling story. As of 2026, rollups handle the majority of Ethereum-ecosystem transaction volume by count. EIP-4844 (March 2024) introduced "blob" data that drastically reduced L2 posting costs, making fees on rollups 10-100x cheaper than L1.

Why it matters

Rollups are where most Ethereum users now live. DeFi, NFTs, and consumer apps increasingly happen on L2; understanding which rollup is which affects fee, security, and bridging risk.

How CryptoRadar24 tracks it

CryptoRadar24 surfaces rollup TVL and growth as part of broader DeFi ecosystem tracking.

Related terms

Layer 2 (L2)
A network built on top of a base blockchain (Layer 1) to provide faster, cheaper transactions while inheriting L1 security.
Gas fee
Transaction fee paid to network validators on Ethereum and similar blockchains, denominated in the chain's native token.
Total Value Locked (TVL)
Aggregate value of crypto assets deposited in DeFi protocols.

FAQ

Are rollups secure?

They inherit security from the L1 they post to (typically Ethereum) — assuming their proof systems are sound. Optimistic rollups have additional risk during the challenge window; ZK rollups carry circuit-bug risk.

Optimistic vs ZK rollup — which is better?

Trade-offs. Optimistic: simpler, longer withdrawal times (~7 days). ZK: faster finality, more complex tech, historically more expensive proofs. Both are mature and widely used as of 2026.

Is Polygon a rollup?

Polygon PoS is a sidechain (independent consensus), not a rollup. Polygon zkEVM is a ZK rollup. The "Polygon" brand spans multiple architectures with different security properties.

How is a rollup different from a sidechain?

Rollups post data and proofs to L1, inheriting its security. Sidechains have independent consensus and security. If the sidechain's validators collude, funds on it can be drained — rollups don't have this risk.