PURPOSE: To provide a fiber structure in the form of a refractory light-weight molding not contg. fibers injurious to health.

CONSTITUTION: This fiber structure is produced by using inorganic fibers, at least 90% of which comprises 20 to 50% wt.% CaO and 50 to 80 wt.% Al2O3, and 10% of which as maximum comprises typical impurity oxides as the balance, using water or a water-contg. liq. as an added lip., and when occasion demands, using an ordinary refractory additive. The fibers which might still exist in the fiber structure are readily decomposed by water or body fluids. Nevertheless, the fiber structure has advantageous thermal and mechanical properties of the ordinary light-weight molding.