I like to tell people I'm a recovering academic. The truth is, though, that I haven't left physics behind. That would be impossible since I've been making a career in the world of building science. So, today I'm going to delve into that subset of building science called building physics as we take a look at the physics of water in porous materials. You'll also learn about the fourth state of water, the one that's not liquid, not solid, and not vapor.