In recent years, wearable interfaces have attracted research attention. As wearing masks has become common worldwide after the appearance of the coronavirus disease 2019, we devised a system to measure facial information from a mask, focusing on facial expressions in this study. Specifically, the expansion and contraction of the mask was measured to classify facial expressions. We conducted classification experiments under various conditions, achieving high classification accuracy, especially for facial expressions in the non-woven fabric mask to which a conductive thread was attached. We found that conductive threads are affordable and easy to sew into masks, and they can be used to construct a wearable interface.
