So I've been curious about thermal conductivity lately, and came across a good reference that showed the conductivity of various materials. http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html It says that air has very poor thermal conductivity (in other words, it acts as an insulator), and is actually so bad that it is the 6th worst on the list. Also on the list were various 'insulators'. Fiberglass, wool insulation, kapok insulation, etc. Now for my question. If air were truly such a great insulator, then why do home builders blow insulation into the walls and in the attic? The whole purpose of insulation is to completely decouple the home temperature from the outside temperature, correct? According to this list, air would do a better job than anything they blow into the walls. What gives?