Waterproof liners are a bit more expensive than conventional padding, but are considered more comfortable by many patients and similar in terms of wear and healing time. For many people, waterproof liners are worth the small incremental cost because of the benefits of ease of maintenance, lowered risk of skin issues, and freedom for bathing and swimming with a cast.
Even if you do not plan on swimming with a cast, not having to worry about whether or not the material gets wet can take a load off of your mind. You do not have to let wearing a cast cramp your lifestyle. Talk with your doctor to see what waterproof liners can do for you, so you can swim with a cast!