In the present paper we combine two analytical frameworks in order to extend our understanding of how students reason about a socio-scientific issue, namely, nanomaterials in consumer products. Using the results from two focus group discussions including seven students each, we first thematically explored undergraduate engineering students' risk perception. Two main themes were found in this analysis: "Exploring the concept of nanotechnology" and "Handling risks with nanotechnology." Second, we analyzed the nature of students' arguments using the SEE-SEP model, which is a coding scheme based on the subject areas Sociology/Culture, Environment, Economy, Science, Ethics/Morality, and Policy, intertwining the three aspects Knowledge, Values, and Personal experience. According to this analysis, 55% of the participants' arguments were based on values, 25% on knowledge, and 20% on personal experiences. Despite the absence of specific knowledge, however, the students could conduct a complex argumentation about nanomaterials and actively examined the paradox of new opportunities but unresolved risks. The students' reasoning reveals that arguments in favor and arguments against the use of nanomaterials in different products do not cross each other out, but co-exist. The results indicate that the risk perception was influenced to some degree by the area of use, such as skin care products or car treatment. It was also found that when lacking specific knowledge, our participants turned to analogies to other technology developments. Implications for education on nanotechnology are discussed.