Some months ago at our monthly meeting, George Swanson, introduced us to the wonders of MgO board. MgO (pronounced em-gee-oh) is magnesium oxide. In China mineral MgO is more common than gypsum. It is used in combination with fibers and other materials to make products that substitute for drywall inside and sheathing or siding outside.
MgO board does not support mold and it does not burn. It is said to hold up to repeated soaking many times better than fiber-cement products. Its takes less energy to produce than portland cement and it is claimed by some to absorb carbon from the air.
At the time of his talk, MgO board was available only by the container load. George had made arrangements with Dragon Board, one of many Chinese manufacturers to import their product. However, it may be available in smaller quantities as its advantages become better known.
For a very complete review of MgO board please see this article: A Primer on the Next Generation of Sheathing by Robert Thomas from Walls & Ceiling Magazine.