Literature in environmental science has documented understudied regions, topics, and the underrepresentation of specific groups in the discipline, with significant consequences for research, policy and advocacy. Understanding inequality as a representation problem is valuable but does not necessarily unpack its mechanisms. Using an epistemic justice lens, I look at scientific instruments as sites of inequality by design in environmental studies. Even when in recent years we have seen an explosion of new scientific tools in the field, how these tools reproduce inequalities is underexplored. The open science hardware movement provides an opportunity for studying this question in practice. I present findings from qualitative research with two projects of the Gathering for Open Science Hardware (GOSH) community in Latin America during 2018–2022. These findings show how researchers use open science hardware to overcome structural inequalities in environmental research. Beyond their lower cost, researchers are using open hardware to enable new ideas and concepts to emerge through flexible and repairable designs. I describe four mechanisms that enable the creation of new epistemic resources: autonomy, flexibility, impact and resilience, and I identify significant limitations to this potential. In the context of ongoing policy discussions promoting wider adoption of low-cost environmental research tools, this work provides insights for seizing the transformative potential of openness towards more fair environmental science.