Recent theoretical models highlight the importance of emotion regulation (ER) flexibility, challenging traditional notions of universally maladaptive versus adaptive strategies. In two independent samples from the USA (158 adults, N = 12,217) and China (144 adults, N = 11,347, analysis preregistered), we employed Ecological Momentary Assessment (EMA) to develop proxy ecological measures for ER flexibility components (context sensitivity, repertoire, feedback responsiveness) and examine their associations with momentary affective outcomes. Participants completed four daily surveys for 21 days, reporting emotional situations, situation characteristics, ER use and change, and momentary distress. Increased momentary context sensitivity and use of repertoire were found associated with reduced distress, while results for feedback responsiveness were less consistent. Maintaining effective strategies was generally adaptive, whereas switching from ineffective strategies was adaptive for momentary depressed but not anxious mood. This novel EMA design demonstrates transcultural similarities in ER flexibility's benefits and nuanced implications of its components on affective outcomes.