This chapter examines the interrelationship between “a market’s materialities and practices” (Geiger and Gross, 2018) by offering an account of how a particular source of energy – wooden biomass – became a perferred energy resource in the Danish energy system. This chapter examines how biomass is qualified, i.e., identified, measured, framed, and, thereby, known. However, the materiality of forests and wooden biomass affords multiple understandings depending on the epistemic equipment – theories, models, and measurements – used. This introduces an epistemic uncertainty in how biomass can be known, providing opportunities for expression and enactment of interests, making policymaking more complex and more contentious. Our analysis highlights the antagonism and power struggles involved in the dynamics of market framing. The chapter concludes with a discussion on how the material ‘unruliness’ of biomass calls for complex accounting methods, leaving biomass incumbents much maneuver room and jeopardizing Denmark’s reputation as ‘a frontrunner’ in energy transition. The chapter contributes to Market Studies research by demonstrating the dual role of materiality in shaping (concrete, situated) interests and valuations while simultaneouly also affecting conditions for future maneuvering/actions. Further, the analysis brings out the politics of valuation.