One reason why caps use for swimming last for a long time is proper care and maintenance. It is important that you rinse it using a cold water right after every use. This simple practice will help prolong the lifespan of your gear. You can do it while you are rinsing your body in the shower or when cleaning your swimsuit.
It is also essential that you dry your cap outside your bag. Let it air dry especially if your cap is made of latex. This will not only prolong the life of your cap, but it will also remove the smell that comes with it when it is wet. Some put baby powder or talcum powder inside the cap.
Do this when it is already dry. The powder will absorb the remaining moisture or water and will make the cap more flexible. This is, however, not applicable to spandex or Lycra caps.