Purpose This paper aims to analyse the general effect of co-created products on the brand equity of observers (OBBE). The influence of different implementations of the co-creation approach on the OBBE is tested. It is also discussed whether co-creation can be a strategic method for companies to positively affect the OBBE in the mass market. Design/methodology/approach A between-subject experiment with a 2 (intensity of integration: democratically voted vs commonly created) × 2 (expert knowledge: no expert knowledge vs expert knowledge) design plus one control group (zero co-creation) is conducted for two brands to test the postulated hypotheses. Findings Co-creation can have a weak positive effect on the OBBE. Integration intensity and expertise of integrated consumer also affect the OBBE only marginally. Research limitations/implications Further research might investigate whether the initial brand equity has a moderating effect. Also brand image and underlying product category could influence the relation between co-creation and the OBBE and would be valuable for future studies. Practical implications Brand managers should aim to convert observers into participants, instead of setting the focus on the presentation of the user-designed product to the mass market. Originality/value This study is one of the few analyzing the effects of co-creation on observers in terms of brand equity. In addition to existing research, the concept of expertise in combination with co-creation and its influence on the OBBE is explored.