Haha, I used the bamboo charcoal foot post bar you mentioned. According to the product description, this kind of foot patch can suck out toxins from our bodies. According to the product description, the more toxins sucked out, the darker the color of the foot pad. When you say gray, it seems that there are not many toxins in your body. Not bad. When I used it, it was black the first day, gray the next day, and then it was useless. Ha ha.