A number of years ago, I was talking with an acquaintance about the use of wood for siding. He said yes, absolutely, but it is important to use only the heartwood if it is not a naturally rot-resistant species. Then, recently, I was outside after a rain and saw this high contrast on the surface of a simple outdoor workbench I had made from a Ponderosa Pine log. I believe the table was about 3 years old when I took the photo. The hydrophilic property of the sapwood is evident, whereas the heartwood remained relatively dry.