How does an ablative heat shield protect a spacecraft during plasma interaction?

The outer layer chemically breaks down, vaporizes, and carries the incoming heat energy away.

Ablative heat shields, utilized in historical missions such as Apollo, are designed as single-use, sacrificial systems. The material, often a composite resin, is engineered to react violently with the extreme heat of re-entry. As it interacts with the plasma, the outer layer undergoes a chemical breakdown process where it vaporizes and chars away. This phase change and material sacrifice consumes the massive incoming heat energy, effectively transporting it away from the spacecraft structure via the gaseous byproducts, thereby keeping the underlying components safe until the material is entirely consumed.