Sustainable Materials: A Conceptual Gap in Definition

The term “sustainable material” has become widely used in materials science, yet its conceptual foundation remains inconsistently interpreted. Despite major progress in sustainability assessment, circularity metrics, life cycle analysis, and policy-oriented frameworks, sustainability is still commonly treated as an intrinsic material property instead of a multidimensional and context-dependent outcome. This perspective addresses this unresolved conceptual gap by critically distinguishing widely used but often interchangeably applied terms such as bio-based, recyclable, biodegradable, circular, green, renewable, and sustainable materials. It is argued that none of these descriptors alone can define sustainable materials, since each captures a specific or only a limited aspect of material behavior while overlooking interacting factors, including processing conditions, infrastructure, embodied impacts, end-of-life management, and application-dependent constraints. Accordingly, the present work challenges binary classification of materials as “sustainable” or “non-sustainable” and proposes a shift toward a more integrated and context- dependent interpretation of sustainable materials. By clarifying the boundaries and limitations of existing terminology, this perspective aims to strengthen scientific communication, improve sustainability-oriented materials selection, and motivate the development of more structured multidimensional frameworks for future “sustainable material” classification.