The present study investigated the relationship between objective temperature and subjective temperature preferences in predicting performance in simple and complex cognitive tasks. We assessed the impact of room temperature (warm and cold) on the ability to “update” (and monitor) working memory (WM) representations in two groups of participants, who differed in their subjective temperature preferences (warm-preferred vs. cold-preferred). Participants performed an N-back task in which conditions (1-back and 2-back) differ in their WM load and cognitive demands. Results showed that the preferred, but not the objective temperature predicts WM performance in the more resource-demanding (the 2-back) condition. We propose that subjective preferences are more reliable predictors of performance than objective temperature and that performing under the preferred temperature may counteract “ego-depletion” (i.e., reduced self-control after an exhausting cognitive task) when substantial cognitive control is required. Our findings do not only favor a cognitive approach over the environmental/physical approaches dominating the research on cognition–environment interactions, but they also have important, straightforward practical implications for the design of workplaces.