Layer 2s & rollups
How do you fit a city's traffic onto one road? Put people on buses.
Analyst · 8 min · Updated 2026-11-08
💡 The shared bus ticket
Instead of 100 people each taking a taxi down a congested highway (Layer 1), they board a bus (Layer 2). The bus pays one toll for everyone and drops a passenger list at the toll booth so anyone can verify who rode. Each passenger pays a fraction of the toll.
How rollups work
A rollup executes transactions off the main chain, then posts compressed transaction data and a state update back to Ethereum. Ethereum acts as the court of final appeal and the place where data is kept available.
Two flavours
| Optimistic rollups | ZK (validity) rollups | |
|---|---|---|
| Assumption | Batches are valid unless challenged | Every batch carries a cryptographic validity proof |
| Withdrawal to L1 | Challenge window, often ~7 days for native bridges | As soon as the proof is verified |
| Trade-off | Simpler, EVM-compatible | Heavier maths, fast finality |
Why fees fell
Dencun (2024) gave rollups cheaper temporary "blob" storage. Fusaka (December 2025) introduced PeerDAS, letting nodes check data availability by sampling small pieces, which allows more blobs per block over time.
Extra risks to understand
- Sequencer centralisation: many rollups still use a single operator to order transactions.
- Upgrade keys: teams can often upgrade contracts; check who controls them.
- Bridges: moving assets between chains has been the source of some of the largest hacks in crypto.
🧮 Practical example: splitting the toll
Key takeaways
- Rollups batch transactions and post data to L1.
- Optimistic = challenge window; ZK = validity proofs.
- Blobs and PeerDAS lower data costs.
- Check sequencer, upgrade-key and bridge risks.
Education only — not financial advice.