Typically "field bales" (bales created on farms with baling machines) have been used, but recently higher-density "precompressed" bales (or "straw-blocks") are increasing the loads that may be supported. Field bales might support around 900 kg per linear meter of wall (600 lb./ lin. ft.), but the high density bales bear up to 6000 kg per linear meter of wall (4,000 lb./lin.ft.), and more. The basic bale-building method is now increasingly being extended to bound modules of other oft-recycled materials, including tire-bales, cardboard, paper, plastic, and used carpeting. The technique has also been extended to bags containing "bales" of wood chips or rice hulls.