Newell and Cousins’ article argues that urban metabolism is a powerful but increasingly fragmented metaphor for understanding how cities consume, transform and discharge materials, energy and ecological relations. The authors identify three distinct “ecologies” of urban metabolism: industrial ecology, which measures urban stocks and flows through tools such as material flow analysis; Marxist ecologies, especially urban political ecology, which interpret metabolism as a socio-natural process shaped by capitalism, power and inequality; and urban ecology, which understands cities as complex socio-ecological systems. Through bibliometric analysis and literature review, the article shows that these traditions have become separate scholarly “islands”, each privileging certain dimensions of urban space while obscuring others. Industrial ecology is strong in quantitative measurement but often treats the city as a black box and neglects politics; Marxist urban political ecology exposes uneven power relations but often privileges the social over the ecological and relies heavily on qualitative methods; urban ecology models complexity but tends to remain politically underdeveloped. The authors therefore propose political–industrial ecology as a way to revitalise the urban metabolism concept by combining the critical spatial and political sensitivity of urban political ecology with the quantitative methods of industrial ecology, such as material flow analysis and life cycle assessment. Their water-supply example illustrates how this approach can reveal the uneven social, ecological and carbon burdens embedded in urban infrastructures. Ultimately, the article concludes that urban metabolism should function as a boundary metaphor, enabling interdisciplinary collaboration without forcing consensus, and helping scholars produce more sustainable, spatially aware and socially just accounts of urbanisation.