Plasma

Intermediate

更新済 Sep 24, 2026

What Is Plasma?

Plasma is an early Ethereum scaling framework that uses a structure of "child chains" built on top of the main chain to process transactions off-chain and ease congestion.

A child chain is a smaller chain anchored to Ethereum by a smart contract that lets each project adapt the structure to its needs.

Plasma was proposed by Vitalik Buterin and Joseph Poon in August 2017 as a scaling solution for Ethereum. Poon also helped design the Lightning Network, which explains the similarities between the two approaches, Plasma for Ethereum and Lightning for Bitcoin, even though their mechanisms differ.

Source: plasmo.io/plasma.pdf

How Plasma Works

The framework is built using smart contracts and Merkle trees, and it allows the creation of many child chains. These child chains run with specific goals that may not match those of the main chain. Users can exit a child chain back to the main chain through a process often called an exit game, which is meant to protect funds if a child chain misbehaves.

Each child chain was typically run by an operator who batched transactions and periodically published a compressed commitment back to the main chain. Users were expected to watch the chain (directly or through a service) and challenge invalid exits within a dispute window. This constant-attention (liveness) requirement was one of Plasma's main usability drawbacks: safety depended on users or their watchtower services acting in time.

Data availability was another structural weakness. Because child chain data lived on the operator rather than on Ethereum itself, users could be left unable to prove their balances if an operator withheld data. This also meant that Plasma could not support general-purpose smart contracts, and child chains were limited to simple structures like payments. Rollups solved this by posting transaction data on Ethereum, making general smart contracts possible while keeping security anchored to the main chain.

Plasma Now

Although the idea was promising, Plasma is no longer Ethereum's main scaling path. The Ethereum documentation states that Plasma was "dropped in favor of layer 2 (L2) scaling protocols," and scaling is now centered on layer 2 rollups.

Now, Plasma is seen as a largely dormant production system because of its operational complexity and how it made general smart contract execution impractical. However, its underlying ideas have not disappeared, as there has been renewed interest in Plasma-style concepts such as exit games for certain narrow use cases. This is best understood as a revival of the design space rather than a return of Plasma as a dominant scaling layer.

Learn more: Blockchain Layer 1 vs. Layer 2 Scaling Solutions

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