>>39 The game mentions that moon rock is a very good conductor of portals, but it also mentions that moon rocks are a) ridiculously expensive and b) poisonous. Also, Cave Johnson didn't discover that moon rocks were good for portals until the tail-end of his career, after portals had been developed and used. I'm guessing that portals set pretty well in any sort of solid, non-reflective rock - most of Aperature seems to be concrete, and the non-portal surfaces look like they're made of metal, glass, or plastic. I'm also thinking that plaster carries portals, since you can shoot portals into the office walls in the game. Wood is a bit iffy, but I'd be willing to accept that relatively smooth wood paneling would carry portals. Since TF2 is in the American desert, which is mostly hard-packed earth, I'm thinking portals would land in the ground pretty reasonably. Too much vegetation (like a strong grass cover or a clump of shrubberies) would probably negate that, though. I HAVEN'T THOUGHT ABOUT THIS TOO MUCH WHAT ARE YOU TALKING ABOUT.