Synonyms for Reflectivity (same or very similar meaning)
WordNet sense 1 (the fraction of radiant energy that is reflected from a surface):
reflectance, coefficient of reflection, reflection factorWordNet sense 2 (the ability to reflect beams or rays):
reflection, reflexionWordNet sense 3 (the capability of quiet thought or contemplation):
reflectivenessFrom the ODE community, based on WordNetadd/edit