Religious activities are no longer confined to local religious communities, but are increasingly taking place online. In that regard, social media is of particular importance for young believers that connect with their peers via platforms such as Instagram. There are conflicting views on the functioning of social media platforms: they are either conceptualized as superdiverse spaces, in which social boundaries can be overcome, or as resulting in separate bubbles that foster exclusive exchanges between like-minded people sharing certain characteristics, including religious affiliation. This article assesses online religious activities based on qualitative research involving 41 young, urban, religious Instagram users of different faiths. We demonstrate how young believers’ interactions on social media produce thematically bound content bubbles that are considerably homogeneous when it comes to religion, but superdiverse in other areas. Religious activities online often have an affirmative effect on religious belonging. This is especially true for young people that perceive themselves in a minority position and search for like-minded people online. We have found that religious content bubbles are clustered around religious traditions. Interreligious exchange (e.g., between Christians and Sikhs) is largely absent, whereas intrareligious boundaries (e.g., between Lutherans, Catholics, and Pentecostals) become blurred. This suggests that differences within religious traditions are losing significance in a digitalized world, while interreligious boundaries remain.