What Is Layer 2?
Layer 2 is a scaling network that processes transactions off the main blockchain and posts the results back to it. Networks such as Arbitrum, Optimism and Base make Ethereum transactions cheaper and faster.
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A Layer 2 is a network that executes transactions outside a main blockchain and then posts the results, plus the data needed to verify them, back to that chain. On Ethereum, well-known examples include Arbitrum, OP Mainnet, Base, zkSync and Starknet; on Bitcoin, the best-known example is the Lightning Network. The goal is to keep the security of the base chain while making transactions much cheaper and faster.
Ethereum mainnet (Layer 1) can only fit a limited number of transactions into each block, so fees spike when demand is high. A Layer 2 bundles thousands of transactions into a single batch and settles it on Ethereum, spreading the cost across many users. The result is that a simple transfer or swap often costs a small fraction of what it would on mainnet.
How does Layer 2 work?
Most Ethereum Layer 2s today are rollups. A rollup executes transactions in its own environment, compresses them and posts them to Ethereum in batches. Ethereum does not re-run every transaction; it stores the batch data, the resulting state and whatever proofs the rollup design requires.
At the center of this process is the sequencer. It collects user transactions, orders them and returns a confirmation within seconds. That quick confirmation is not the same as finality on Ethereum, though: a transaction is only truly settled once its batch has been posted to mainnet and the relevant verification process has run its course.
The Dencun upgrade in March 2024 introduced EIP-4844, which lets rollups post their data to cheaper, temporary storage called “blobs.” Fees on many Layer 2s dropped sharply after it went live.
Optimistic rollups vs ZK-rollups
The two main rollup families prove correctness in different ways:
- Optimistic rollups assume batches are valid unless someone challenges them with a fraud proof during a dispute window. Arbitrum, OP Mainnet and Base work this way, and withdrawals to Ethereum through their official bridges typically take around seven days.
- ZK-rollups attach a validity proof, built with zero-knowledge cryptography, showing that each batch was computed correctly. zkSync, Starknet, Linea and Scroll use this approach, and withdrawals can complete once the proof is verified on mainnet.
Despite the name, ZK-rollups are not privacy networks. On most of them, every transaction is visible on a public block explorer; the cryptography is used to prove computation, not to hide it.
Layer 2 vs sidechain: what’s the difference?
A sidechain is a separate blockchain with its own validators and its own consensus rules. It connects to Ethereum through a bridge, but it does not inherit Ethereum’s security: if its validators misbehave, Ethereum cannot step in.
A rollup, by contrast, posts its data and proofs to Ethereum so that, by design, users should be able to withdraw to mainnet without trusting the sequencer. In practice, many rollups still rely on admin keys and upgradeable contracts. Independent trackers such as L2BEAT rate each network on how far it has moved toward full decentralization.
How to move funds from Ethereum to a Layer 2
- Find the right network. Check the official site of the app you want to use to see which Layer 2 it runs on.
- Add the network to your wallet. Use network details (RPC, chain ID, explorer) from official documentation or a trusted network list, and ignore “add network” prompts from sites you don’t know.
- Choose how to get there. You can use the official bridge, or withdraw directly from an exchange that supports that Layer 2. A direct exchange withdrawal is often the cheapest and simplest route.
- Hold ETH for gas. On Arbitrum, OP Mainnet and Base, fees are paid in ETH. Without ETH on the destination network, you won’t be able to move your tokens.
- Send a test amount first. A small first transfer confirms that the network and address are right.
Your wallet shows the same address on Ethereum and on its Layer 2s, but the balances are separate. Switching networks in your wallet doesn’t move anything; it only changes which chain you’re looking at. Our guide to choosing the right crypto network covers this in more detail.
Is Layer 2 actually cheaper? Working out the total cost
Comparing per-transaction fees alone can mislead you. Take a hypothetical case: bridging from mainnet costs $6, a swap on the Layer 2 costs $0.10, and bridging back costs $3. A single swap then costs $9.10 in total. If the same swap costs $5 on mainnet, mainnet is cheaper for that one-off trade.
If you plan to make many transactions on the same network, though, the entry and exit costs are spread across all of them and Layer 2 quickly comes out ahead. These numbers only illustrate the math; real costs depend on network demand, transaction type and current gas fees.
Why do Layer 2 withdrawals take so long?
On optimistic rollups, withdrawals through the official bridge must wait out the challenge period, which is why moving funds within a Layer 2 takes seconds while returning to Ethereum can take days. On ZK-rollups, the wait depends on how quickly proofs are generated and verified on mainnet.
Third-party fast bridges cut this to minutes by paying you from their own liquidity on the destination chain. You pay an extra fee for the convenience and take on the smart contract risk of that bridge. For larger amounts, it’s worth deciding in advance which route you’ll use.
What to check before using a Layer 2
- Token version: A token on a Layer 2 may be the issuer’s native version or a bridged representation. With stablecoins such as USDC, check which one you’re receiving.
- Outage plan: If the sequencer goes down, transactions can stall. Check the docs to see whether the network offers a forced-inclusion or escape route via mainnet.
- Signing hygiene: Low fees do nothing to reduce the risk of fake contracts or phishing. Read the recipient, amount and permissions on every signature.