What is blobspace and how does it lower rollup fees

26 October 2026

Blobspace is the portion of Ethereum blocks reserved for temporary data blobs that rollups use to post transaction data. It lowers rollup fees by providing a cheaper, separate storage area than the permanent calldata space on Ethereum’s execution layer. Rollups that post data to blobs pay significantly lower fees than those using calldata, and this difference is the core mechanism behind recent fee reductions for many Layer 2 networks.

How Blobspace Works

Ethereum blocks have two distinct areas for data. The execution layer contains calldata, which is permanently stored in the block and available for anyone to read. Blobspace, introduced in the Dencun upgrade, exists in a separate part of the block called the beacon block. Blobs are large pieces of data - each blob holds roughly 128 kilobytes - that are stored only temporarily. Ethereum nodes keep blobs for about 18 days, after which they can be safely discarded.

A rollup posts transaction data to Ethereum in either calldata or blobspace. When using blobs, the rollup sends a commitment to the data (a hash) to the execution layer, while the actual blob data is stored in the beacon block. Validators can verify the blob data matches the commitment, but do not need to store it permanently.

Why blobspace costs less

Calldata is expensive because it competes for the same block space as regular Ethereum transactions and smart contract executions. Every byte of calldata must be permanently stored and processed by every node. Blobspace is cheaper for several structural reasons:

• Blobs do not compete with execution layer transactions for gas. They have their own fee market with a separate base fee.
• Blobs are only stored temporarily, reducing long-term storage costs for validators.
• The Ethereum protocol caps the total blob data per block at 6 blobs (about 768 kilobytes), which is roughly six times the calldata capacity of an average block. This larger supply drives down per-byte costs.

The fee for posting a blob is calculated using a separate fee mechanism called blob gas. Blob gas has a base fee that adjusts based on demand for blobspace, similar to how Ethereum’s regular gas price adjusts. A rollup posting one blob typically pays a fraction of what it would pay to post the same data as calldata.

How this lowers rollup fees

When a rollup reduces its cost to post data to Ethereum, it passes those savings to users. The direct effect is visible in transaction fees on Layer 2 networks that have adopted blob posting. Here is the sequence:

1. A rollup batches hundreds or thousands of user transactions into a single batch.
2. Instead of posting the batch data as calldata, the rollup compresses the data and posts it as one or more blobs.
3. The rollup pays the blob gas fee, which is lower than the equivalent calldata fee.
4. The rollup operator updates its fee model to reflect the lower data posting cost.
5. User transaction fees drop proportionally.

The size of the fee reduction depends on how efficiently the rollup compresses data and how many blobs it uses per batch. Networks that batch aggressively and compress well can see fees drop by 90% or more compared to pre-blobspace costs.

Which rollups use blobspace

Not all Layer 2 networks use blobspace. Adoption depends on the rollup’s architecture and whether it has implemented the necessary protocol changes.

• Most optimistic rollups like Arbitrum One and OP Mainnet post data to blobs. They switched shortly after the Dencun upgrade.
• ZK rollups such as zkSync Era, Scroll, and Starknet also post proofs and data to blobs. Their fee reductions depend on proof size and compression efficiency.
• Some rollups, particularly those using alternative data availability layers like Celestia or EigenDA, may not use Ethereum blobspace at all. They post data to their own DA layer and only post a proof to Ethereum.

A rollup that uses blobspace will typically show a “blob” transaction type on block explorers. You can check whether a specific rollup uses blobs by looking at its transaction data in a block explorer under the “blob” or “data” section.

Trade-offs of Blobspace

Blobspace is not free. There are practical limitations:

• Blobs expire after about 18 days. If a rollup’s data is needed for longer, it must archive blobs elsewhere.
• Blobspace has a maximum capacity of 6 blobs per block. During high demand, blob fees can spike. In periods of heavy rollup activity, blob base fees can rise to levels comparable to calldata fees.
• Rollups must maintain their own data archiving to ensure long-term availability. This adds operational complexity.

For most users, the trade-off is positive: fees are lower most of the time, and the temporary storage is sufficient for typical rollup security guarantees. For applications that require permanent on-chain data, calldata remains an option, though at higher cost.

How to estimate blobspace fees

Blob gas prices are visible on Ethereum block explorers and dedicated blob fee trackers. The base fee for blob gas adjusts every block based on demand, just like execution gas. You can look up the current blob base fee on sites like Etherscan or Dune Analytics. Rollup operators typically publish their current fee models, which include the blob gas component. Checking the rollup’s documentation or fee page is the most reliable way to understand what you will pay.

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