How can individuals in organizations become agents of divergent change if they are constrained by the very institutions they seek to change? Previous work has touted experimental spaces as potential remedy to this ‘paradox of embedded agency’. Yet, it remains a puzzle how such experimental spaces enable or constrain the change efforts of employees in the context of social innovation in for-profit firms where such change efforts challenge the dominant market logic. To shed light on this question, we conduct a multiple case study (including 40 interviews) examining four social intrapreneurship programs as dedicated spaces for social innovation. We derive a theoretical model depicting the ‘social innovation sandbox’ in which employees get to play with their social innovation ideas at the organizational periphery, while the protective boundaries of the experimental space impede these ideas from diffusing to the organizational core. Our findings contribute to research on social innovation and intrapreneurship, experimental spaces, and hybrid organizing.