The actual source of coronal heating is one of the longest standing unsolved mysteries in all of astrophysics. The million degree corona requires a permanent heating mechanism, or the gas would cool down in about an hour. Solar physicists agree that this mechanism involves the Sun's magnetic field, but few agree on the details of how magnetic energy in translated into thermal energy. Coronal loops, their structure and sub-structure, their temperature and density details, and their evolution with time, hold the key to understanding this coronal heating mystery. A loop had always been thought of as a simple magnetic flux tube, where each position along the loop is characterized by a single temperature and density. Recent results, however, found that this simple picture could not explain the observations and a multi-thermal analysis was required. If we picture the loop as a tangle of magnetic strands instead of single flux tube, then the multi-thermal result is expected and even predicted by some classes of coronal heating models.