As previously stated in response to yesterday's and today's thread there are many types of OSB, and Structurwood is one of those types. The quality of the product is at the other end of the spectrum compared to standard OSB sheathing. It was, when my coach was built, one continuous sheet on each floor level so that there are no butt joints. Sheathing OSB is strong (somewhat) only when supported perpendicular to the grain, or orientation. Structurwood is much stronger and has far more resins impregnated in the wood. The alternative is plywood, and that tends to delaminate when subjected to constant moisture, and is generally not available in long sheets like Structurwood. As a builder I stopped using plywood on subfloors when Structurwood, and similar products like Advantech, first appeared on the market. These are not cheap alternatives to plywood, some actually cost more, and they tend to perform better. The really bad wood product used in mobile homes and stick-built homes in the 70's and early 80's was MDF, or similar names, and was sawdust glued with a minimal amout of resins. It normally doubled in thickness when saturated and then crumbled when dried. High humidity was lethal to that junk, but what Heartland is using is a good product.