["The British Journal of Sociology, EarlyView. ", "\nABSTRACT\nPatterns of volunteering have predominantly been explained by focusing on the supply side in terms of volunteers' resources and motivations. We shift the focus to the demand side of volunteering and develop the concept of demand networks. We argue that experienced demand for help in one's personal network is important to explain why individuals engage in informally organized voluntary help and support: the amount of demand for help a person experiences in their network influences the likelihood that the person helps. To explain why individuals who perceive similar levels of demand do not all volunteer to the same extent, we theorize how demand networks are mediated by the institutional factors of social values and gender roles. We hypothesize that altruistic values and gendered social roles dispose individuals to respond differently to demands for help, with women and those holding stronger altruistic values being more likely to act on the needs they perceive. We examine the hypotheses using a cross‐sectional survey inquiring about informally organized volunteering during COVID‐19. The results clearly indicate the importance of the demand side to adequately explain informal volunteering. We argue that our findings imply that sociologists should reconceptualise social connections not only as providing access to resources but also as a source of demands on individuals. In doing so attention should be paid to gender roles which the results suggest function as an amplifier of demand networks association with informal volunteering. We further discuss how the results have implications for building social capital and societal resilience in times of crisis.\n"]