Methods are disclosed in which two or more forming chambers are used to process inorganic fibers by gravity-laying methods. The methods may comprise using a first forming chamber to open inorganic fibers and using a second forming chamber to process the opened inorganic fibers, optionally to blend the opened inorganic fibers with additional inorganic fibers and/or with particulate additives, and to collect the inorganic fibers as a mat. The methods may comprise using a first forming chamber to form a first inorganic fiber layer and a second forming chamber to form a second inorganic fiber layer, and consolidating the first and second inorganic fiber layers so as to provide a multilayer gravity-laid inorganic fiber web.