Urea nitrate (UN) has not found use as a legitimate explosive but is commonly used as an improvised explosive. The dehydration product of UN is nitrourea (NU). Visually both UN and NU are white solids that both melt around 160 degrees C. Other properties differ markedly as might be expected from an inorganic salt (UN) and an organic molecular compound (NU). An extensive physical characterization of NU and UN is reported. Two reported routes to the NU product are compared and a decomposition mechanism of UN proposed.