In this mask, green tea infusion is used as the water phase instead of plain water. That means the entire liquid portion of the product carries the soluble compounds from green tea — primarily polyphenols such as catechins (including EGCG) — which are widely studied for their antioxidant and soothing properties in cosmetic formulations.
Practically, this helps counterbalance the astringent sensation of volcanic clay. While the clay absorbs sebum and lifts surface residue, the green tea infusion contributes a calmer, less "stripped" after-feel. It does not turn the mask into a treatment serum; the contact time is short (rinse-off), so absorption is limited. Think of it as a formulation choice that makes the cleansing step more comfortable, especially for combination skin that gets oily but still reacts to harsh cleansers.
There is no disclosed concentration percentage, and the infusion is not a substitute for a dedicated leave-on antioxidant product. If you already use a green tea serum or toner, this mask complements it by not undoing that care during the cleansing step.