Environmental claims are increasingly used for consumer goods, renewable energy and building materials – and so is greenwashing. Prior research has looked at its impact on consumer trust and behaviour, but has not examined why some consumers are more susceptible than others. The paper contends that susceptibility to greenwashing is a function of circumstances, because financial duress, time constraints, and emotional or health stressors drain cognitive bandwidth, the mental capacity necessary to assess complex, ambiguous, or unsubstantiated environmental claims. Drawing on consumer vulnerability theory, scarcity psychology, research on green consumer confusion, and the Hunt–Vitell theory of marketing ethics, the paper offers a conceptual model and seven testable propositions linking vulnerability, bandwidth depletion, green consumer confusion, ethical evaluation and consumer well-being. It also links the model to Directive (EU) 2024/825, showing how a bandwidth-informed perspective can inform the regulation of environmental claims, marketing of green technologies and environmental communication and education