Conductive material requires two conditions, 1,. Charged particles. Two particles are free to move NaOH are ionic crystals, by the anion and cation composition, but these ions are trapped in a balanced ionic bond position, vibration, can not move freely and therefore can not not be conductive solid NaOH. After melting, the heat damaged the part of the ionic bond, NaOH ionize and become a free movement of Na + and Cl-, can be a conductive.