Most people are not aware of that masks need to be replaced frequently, especially with excessive wear. To address this problem, the design team came up with a smart and convenient solution. An invisible QR code printed on the surface of a Time to Change mask begins to appear as the exposure to dirt increases. The visibility of the QR code indicates that one needs to change the mask. The mask can also be ordered by scanning the QR code directly. This design not only focuses on mask design, but also connects customers and merchants in a clever way, therefore improving the whole user experience of the product, while simplifying the direct sales route and the promotion of the product.