What is a blob transaction?
- Author
- CRYPTO PORT Editorial
- Published
- Updated
- Reading time
- 5 min
In short
A blob transaction is a dedicated Ethereum transaction type that attaches a large chunk of data to a block. The blob itself cannot be read by the EVM, and nodes drop it after a fixed period. Rollups use it as a cheap place to post their transaction data.
Key points
- A transaction type that attaches a large data chunk to a block
- The EVM cannot read the contents, only a commitment hash
- Nodes prune it once the retention period passes
- Priced in its own fee market, separate from ordinary gas
Definition
A transaction type added by EIP-4844 that attaches bulk data — a blob — which contracts cannot read, and which the network retains only for a limited period.
Each blob is roughly 128 kilobytes, and an Ethereum block can carry several of them. The contents are handled outside the execution layer, and contracts can reference only a hash derived from a KZG commitment. The design accepts that proving the data exists is enough — the EVM never needs to read it.
The crucial point is that blobs are not permanent storage. Consensus layer nodes are allowed to delete blobs once the retention window passes, and the chain still verifies afterwards. Anyone who needs older transaction history has to pull it from their own archive or a third-party one.
Blob space is priced in a market of its own, independent of ordinary gas. The fee rises exponentially when block usage exceeds the target and falls when it is below, so rollup fees can move with blob congestion rather than with the regular gas price.
Watch out for
- · Blobs are not permanent, so looking up old data depends on a separate archive
- · Blob fees move independently of ordinary gas, and L2 fees alone can spike during congestion
- · Contracts cannot read blob contents, so the data is not usable on-chain directly