Policy makers are under political pressure to adopt policies that achieve net-zero greenhouse gas emissions. Reaching net zero is a demanding challenge requiring durable policies that last; that is, withstand short-term turbulence. However, there is a lack of clarity in the existing literature on both the conceptual meaning of policy durability and its empirical manifestations. This paper distinguishes between three central dimensions of policy durability and uses them to shed new light on the long-term evolution of EU climate policy. It reveals that the EU has addressed the relationship between policy durability and policy flexibility by working iteratively across and between different policy elements (instruments, programmes, goals, etc.). In revealing these patterns, it addresses a greatly neglected feature of policy design processes: the dialectical relationship between durability and flexibility.