An insulation structure such as a cover provides desirable heat insulation for a heated metal container such as a ladle. The insulation structure is assembled in a manner affording ease of subsequent repair in high-wear areas of ceramic fiber insulation. The ceramic fiber insulation is at least partly in bundled form and the bundles are generally positioned so that fiber blankets are oriented in different directions in the structure, yet the fiber is all in snug fit and achieves highly efficient insulation.