The role of cross-cutting exposure in political polarization has long been discussed. Building on this literature, we proposed a moderated mediation model in which cross-cutting exposure is linked to political polarization, especially affective polarization, differently through different types of political expression, and furthermore these indirect effects of cross-cutting exposure are moderated by opinion climate perception. To test this model, we used data collected by a multi-method approach in the context of a South Korean presidential election: (a) digital trace data of online discussion behavior (i.e., exposure and expression) in the online discussion forum custom built for this study, combined with (b) traditional three-wave panel surveys. Results indicate that cross-cutting exposure increased cross-cutting expression while having no effect on like-minded expression. Cross-cutting expression was then found to reduce affective polarization and attitude extremity. Furthermore, the mediation by cross-cutting expression between cross-cutting exposure and attitude extremity was amplified when participants perceived their opinion to be on the majority side, but such moderation effect was not significant on affective polarization. Implications were discussed regarding ‘hearing the other side’ and ‘speaking the other side.’