A method of treating tough inorganic fiber bundles including opening a plurality of the tough inorganic fiber bundles such that tough inorganic fibers can be dispersed in a liquid slurry to lay down a homogenous fiber aggregate, wherein the tough inorganic fibers have a crush settle volume of greater than 250 ml, optionally greater than 450 ml. Also, a method of treating tough inorganic fiber bundles including dispersing a plurality of the tough inorganic fiber bundles in a slurry with a dilution of about 0.1% to about 2%, optionally about 0.1% to about 1%, effective to lay down a homogenous fiber aggregate, wherein the tough inorganic fibers have a crush settle volume of greater than 250 ml, optionally greater than 450 ml.