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.

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.

A holding material includes a stack of a first mat and a second mat, the first mat including alumina fibers that include 60 wt % or more of alumina and 40 wt % or less of silica, and the second mat including silica fibers that include 60 wt % or more of silica and 40 wt % or less of alumina and having a surface pressure higher than that of the first mat as measured at a gap bulk density of 0.30 g/cm.sup.3.

The present invention relates to a mounting mat for mounting a pollution control device in a catalytic converter, the mounting mat comprising a non-woven mat of inorganic fibers having distributed therein inorganic particles having an average diameter of 1 nm to 100 nm and wherein the mounting mat is free of organic binder or contains organic binder in an amount of not more than 5% by weight, based on the total weight of the mounting mat. The invention further relates to a pollution control device including the mounting mat and to a method of making the mounting mat.

Provided are an inorganic fiber-formed article having both high basis weight and excellent peel strength and a mat for an exhaust gas cleaning apparatus and an exhaust gas cleaning apparatus including the inorganic fiber-formed article. The inorganic fiber-formed article includes inorganic fibers and needle marks extending in the thickness direction and including vertical bundles composed of the inorganic fibers extending in the thickness direction, in which the average volume of the vertical bundles per needle mark measured by a prescribed peel test is 1.0 mm.sup.3 or more.

A holding material includes a stack of a first mat and a second mat, the first mat including alumina fibers that include 60 wt % or more of alumina and 40 wt % or less of silica, and the second mat including silica fibers that include 60 wt % or more of silica and 40 wt % or less of alumina and having a surface pressure higher than that of the first mat as measured at a gap bulk density of 0.30 g/cm.sup.3.

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.