British Household Panel Survey data are used to show that individuals giving up resources for others are associated with communities with less social vices (higher levels of social capital). Analysing resource flows between people offers a new way of evaluating social capital and its determinant factors. Transfers between persons are further analysed using descriptive economic models. Social norms, networks, relative resource endowments and reciprocation all affect resource flows, but altruism determines whether relationships become mutually beneficial and supportive or else extractive and polarising. Positive social capital is characterised by individuals investing resources in people not better off than themselves. Copyright © 2013 John Wiley & Sons, Ltd.