The negative footprint illusion (NFI) refers to the counterintuitive tendency to judge a mixture of environmentally friendly and conventional items as producing less total impact than the conventional items alone. Although typically attributed to intuitive averaging processes, little is known about the conditions under which this bias emerges. Across two experiments using housing and packaging stimuli in recycling-relevant judgment contexts, the NFI appeared reliably under conditions that reduced support for explicit summation, most clearly at larger set sizes, but was absent when additive evaluation remained tractable. The effect generalised across item categories and domains and persisted even when recyclable and non-recyclable materials belonged to different categories, such as bottles and cans. Affective evaluations (valence and arousal) and behavioural intentions did not predict individual differences in illusion magnitude, providing little support for affective-halo or moral-compensation interpretations. Instead, the findings support a cue-integration account in which “green” and “brown” signals are combined into a single composite impression rather than summed. These results extend the NFI to recycling judgments and demonstrate that intuitive averaging processes can distort perceived environmental impact in everyday decision-making.