Insights into how consumer attitudes toward nanotechnology are formed and develop are crucial for understanding and anticipating possible barriers in consumer acceptance of nanotechnology applications. In this study, the influence of affect and cognition on overall opinion is investigated longitudinally for emerging nanotechnologies, and compared with conventional technologies. Overall, in attitude formation toward nanotechnology applications, people rely relatively more on affect than cognition. Over time, reliance on affect decreases whereas reliance on cognition increases for nanotechnology. This suggests that over time nanotechnology applications have become somewhat more integrated within people’s already existing knowledge structure. However, for conventional technologies the influence of affect and cognition on overall attitude remains stable over time. The current study shows that it is essential to address both affective and cognitive aspects of public opinion of nanotechnology.