This paper studies, both theoretically and experimentally, frame effects in the context of a strategic situation in which players have to make a costly contribution either i) to achieve or ii) not to loose a non excludable monetary prize (i.e. a public good). By contrast with related works on framing in public good situations, our experimental protocol lead to public good provision (not deterioration) only if a certain contribution level is achieved. In this respect, we find that a) subjects' behavior is highly sensitive to framing effects and that ii) which frame leads to higher contribution schedule crucially depends on the contribution schedule. We apply Prospect Theory to intepret our experimental findings, calibrating the equilibria to the parameter models which better suit our experimental evidence.