A retaining material that can sufficiently maintain the function of retaining a pollution control element in a pollution control device at high temperature. In one aspect, the retaining material has a mat shape and contains inorganic fiber material, with the retaining material containing: a surface layer containing inorganic colloid particles; and an internal region positioned further to the inside than the surface layer, impregnated with inorganic colloid particles and organic binder; wherein the surface layer contains inorganic colloid particles at a higher concentration than the internal region; and the amount of inorganic colloid particles in the internal region is 1 mass % to 10 mass % based on the total mass of the retaining material.