My shop landlord used thermo modified poplar to side his house. The wood milled very well, doesn't seem to want to warp, and is rot and insect resistant without paint or treatment. I have used some of his scrap to make small items. It cuts cleanly, mills like butter and doesn't seem to have any internal stress. The site linked above is wrong about the odor being that of wood, it smells like a smoke house when you cut it. The odor dissipates after while. The poplar looks like walnut and, in fact, when finished with BLO is hard to tell it from walnut.