Layer 1 vs. layer 2 vs. sidechains
Three ways to build on or beside a blockchain, and the one question that separates them: who keeps your money safe?
A layer 1 is a base blockchain with its own security, like Bitcoin or Ethereum. A layer 2 processes transactions separately but relies on the layer 1 to keep funds safe: if the layer 2's operators misbehave, users can still get their money back through the layer 1. A sidechain is a separate blockchain with its own validators, connected by a bridge; if its validators misbehave, the layer 1 can't save you.
Layer 1: the base chain
A layer 1 has its own consensus, its own nodes and its own coin to pay fees. Bitcoin, Ethereum, Solana, Cardano and Avalanche are all layer 1s. Each makes its own trade-off between speed, cost and decentralization (see the trilemma).
Layer 2: borrowing the base chain's security
The test for a true layer 2 is simple: can you get your funds out through the layer 1 even if the layer 2's operators disappear or cheat?
- Rollups (on Ethereum: Arbitrum, Optimism, Base, zkSync, Starknet, Linea) post their transaction data to Ethereum along with fraud proofs or validity proofs. Ethereum's rules protect the funds.
- Payment channels (on Bitcoin: the Lightning Network) let two parties exchange many payments off chain and settle the final balance on Bitcoin. Either side can close the channel on chain if the other stops cooperating.
In practice many rollups still have "training wheels": a small council can upgrade the contracts, so you're partly trusting them. Independent trackers such as L2BEAT grade this as Stage 0, 1 or 2.
Sidechains: separate chains, linked by a bridge
A sidechain is its own blockchain with its own validators that runs alongside a main chain. You move funds over a bridge, and the sidechain's validators, not the main chain, decide what's valid.
- Polygon PoS has its own proof-of-stake validators and posts periodic checkpoints to Ethereum.
- Liquid is a Bitcoin sidechain for faster settlement and confidential amounts. Bitcoin moved onto it is held by a federation of member companies.
- Rootstock is a Bitcoin sidechain for smart contracts, secured by Bitcoin miners merge-mining it, with its bitcoin peg also managed by a federation.
Side by side
| Compare | Layer 1 | Rollup (L2) | Sidechain |
|---|---|---|---|
| Who checks transactions | Its own nodes | Its sequencer, with proofs checked on the L1 | Its own validators |
| Where the data lives | On itself | Posted to the L1 | On itself |
| If operators cheat | Needs a majority attack | Users can exit through the L1 (once mature) | Funds can be lost |
| Fees | Set by its own demand | Usually far lower than the L1 | Usually low |
| Examples | Bitcoin, Ethereum, Solana | Arbitrum, Base, zkSync | Polygon PoS, Liquid, Rootstock |
Example: the same USDC, three places
You hold 100 USDC on Ethereum, on Base and on Polygon PoS. All three show "USDC" in your wallet. On Ethereum, it's protected by Ethereum itself. On Base, it's protected by Ethereum plus the rollup's contracts and upgrade council. On Polygon PoS, it's protected by Polygon's validators. They're three different networks, and sending to the wrong one is a classic mistake: see sent crypto to the wrong network?
Limitations
- Labels are marketing as often as engineering. Check what a network actually does before trusting the "layer 2" badge.
- Moving between layers costs fees and time, and every bridge adds risk.
- Liquidity and apps are split across many networks, which makes it easy to end up with tokens stuck where you can't use them.
Frequently asked questions
Is Polygon a layer 2?
Polygon's original PoS chain is better described as a sidechain: it has its own validators and posts checkpoints to Ethereum. Polygon also builds zero-knowledge technology, so check which Polygon network you mean.
Is the Lightning Network a layer 2?
Yes. It's a network of payment channels on top of Bitcoin, and either party can settle on Bitcoin if the other stops cooperating.
Is Solana a layer 2?
No. Solana is a layer 1 with its own validators and consensus.
Are layer 2s safer than sidechains?
Generally, if the rollup is mature, because users can exit through the layer 1. Many rollups still have upgrade councils, so the gap is smaller than the labels suggest.
Do I need different coins on each layer?
You need that network's gas token. On most Ethereum layer 2s that's ETH; on Polygon PoS it's POL.
Where to next
Sources
- Layer 2 (ethereum.org)
- Sidechains (ethereum.org)
- Scaling (ethereum.org)
- Lightning Network paper (Poon and Dryja)
- Liquid Network documentation (Blockstream)
- L2BEAT: rollup stages
Written for beginners and checked against the sources listed. Last reviewed November 4, 2026. This page is educational and is not financial, tax or legal advice. How we write and check pages.