Although social influence on consumers’ behaviour has been recognized and documented, the vast majority of empirical consumer studies about sustainable products considers mainly, if not only, individual characteristics (socio-demographic attributes, individual environmental attitudes, etc.), to explain the decision to buy sustainable products. Making use of experimental methods, this paper studies the social influence that peer groups like colleagues, family and friends may exert in the decision to choose for environmentally friendly products rather than conventional ones. We also test for different types of social influence, in particular for ‘herd behaviour’ vs. ‘social learning’. In our experimental setting, the relevance of peer effects is corroborated. We find clear evidence for ‘herd behaviour’ and the data indirectly support the presence of ‘social learning’ effects. The results also suggest heterogeneous impact of specific social groups.