I just cleaned our Novurania which I believe is Hypalon. Previous owners health issue had left it in the elements for three years before I aquired it. I used West Marines Inflatable cleaner, Dawn, bleach and three tries with the Magic Erasor. Finally it was almost new looking. I then used two coats of WM's Inflatable Protector stuff and it is looking good and even shines a bit. The chalk and most of the mold stains are gone. It was a good bit of work but it's doable. I've heard Aurora has a good restoration product also. Now we keep it covered.