Consumers are often confronted with incomplete product information. In such instances, they can eliminate the product from further consideration due to higher associated uncertainty or ask for more information. Alternatively, they can apply subjective theories about covariation to infer the value of missing attributes. This paper investigates the latter option in the context of sustainability and provides an in-depth exploration of consumers' inference formations. Drawing from rich qualitative data, it offers a conceptualization of the underlying relationships consumers use to infer product sustainability based on other product attributes. The study further assesses whether these findings can be captured in a quantifiable way. To this end, inferred sustainability is conceptualized as a formative second-order construct, thereby depicting the influence of inference-triggering product attributes.