I think some of you guys are mistaking OSB with the old particle board that was/is used in cheap furniture. Particle board looks like sawdust formed in large sheets. Once wet the stuff will swell and begin to disintegrate into what is almost powder. OSB on the other hand is a composite wood but is large flakes of wood, maybe and inch or so in diameter, that are stranded flat sides down and layered on each other. Prior to layering, these flakes are coated with glue/epoxy/adhesives that are water resistant or water proof. Heated presses are used to put terrific pressure and heat to produce sheets of stranded board.
It is much, much better than the old particle board. It is also better as sheeting for roof construction in house building than the old 1/2 inch plywood that could have areas with no glue and/or voids between layers.