Researchers have discovered a negative thermal expansion material that shrinks by a record-breaking amount when heated, and which could help control materials’ thermal expansion. The volume of the reduced ruthenate material shrank by 6.7 percent, more than double that seen for the current record-holder, but this could not be explained by atomic changes. Microstructural effects resulting from highly anisotropic thermal expansion of the crystal grains are believed to trigger this colossal bulk negative thermal expansion.