Informational social support can have both positive and negative effects on employees. This research aims to examine the curvilinear relationship between informational social support and employees' cognitive processes, specifically cognitive depletion and creativity. Additionally, we investigate the moderating role of emotional stability on this curvilinear relationship, particularly regarding cognitive depletion. A total of 108 male employees in South Korea participated in the study, completing 864 two-wave, time-lagged daily diary questionnaires. The surveys measured informational social support, cognitive depletion, creativity, and emotional stability. The findings reveal that informational social support enhances employees' cognitive processes up to a certain threshold, after which its effects become detrimental, demonstrating a curvilinear pattern. Furthermore, emotional stability moderates this relationship: emotionally stable employees show a linear relationship between informational social support and cognitive depletion, while emotionally unstable employees exhibit a curvilinear relationship. Our results suggest that excessive informational social support may harm employees' cognitive processes, indicating that there is an optimal level of support, beyond which the effects become counterproductive.