It should be, but often it is not. Some pillow manufacturers claim their pillows to be waterproof when they are no more than water-resistant. We have seen complaints that their pillow protector was not waterproof when a puppy urinated on it – or even when a toddler urinated on it. While pillow protectors may be constructed to resists drooling, sweat and occasional small spillages, they are not made for dogs to pee on. Nor are they made for toddlers to pee on. That would be your responsibility, not that of the pillow cover vendor. If you believe that to be a risk, then you could cover the pillow in cling film then put it all into one of our pillow protectors. This would provide you will a more comfortable sleeping surface.