People consistently act in ways that harm the environment, even when believing their actions are environmentally friendly. A case in point is a biased judgment termed the negative footprint illusion, which arises when people believe that the addition of “eco-friendly” items (e.g., environmentally-certified houses) to conventional items (e.g., standard houses), reduces the total carbon footprint of the whole item-set, whereas the carbon footprint is, in fact, increased because eco-friendly items still make a contribution to the overall carbon footprint. We present a study that explores whether people’s susceptibility to the negative footprint illusion is associated with individual differences in: (i) general reasoning dispositions measured in terms of actively open-minded thinking, impulsivity and reflective reasoning (indexed using the Cognitive Reflection Test; CRT); or (ii) environment-specific reasoning dispositions measured in terms of compensatory green beliefs and environmental concerns. We demonstrate a negative footprint illusion when participants rated the carbon footprint of conventional houses combined with eco-friendly houses; however, the illusion did not extend to participants’ ratings of the carbon footprint of apples. Environment-specific dispositions were also found to be unrelated to the negative footprint illusion. Regarding general dispositions, our study revealed an association between actively open-minded thinking, measured on a seven-item scale, and reduced susceptibility to the negative footprint illusion. However, an ability to engage in more reflective thinking, assessed using the CRT, was not associated with reduced susceptibility to the illusion. Our findings provide only limited evidence for individual variation in reasoning dispositions playing a role in differential susceptibility to the negative footprint illusion, suggesting that the basis of individual differences in such vulnerability may reside in other person variables, perhaps ones relating to fundamental cognitive factors (e.g., working memory capacity).