Cap with Time / PET Bottle Cap

When we use a bottle to drink, we sometime forget how long the content has been exposed to air.
The amount of germs grow more and more quickly with the time passing.
This design can easily give a visual to users about how long the bottle has been opened.
After the bottle being opened, the color on the cap began to turn red because of the air contact. The longer time passes, the more extended color it may appear on the cap.