The blankets can have a waterproof treatment. A thin layer will be set up on the outside of the blanket. This treatment is only possible on original outdoor blanklets, so not on stable blankets or cotton blankets. There is no warranty for the waterproof blankets (even not after the treatment). Because there are sold blankets of less quality. Besides this the condition of the blankets is also important. The blanket will be worn out by using it like biting by other horses, scraping, rolling etc.