There is “waterproof” sunscreen that we can all attest, due to bad sunburns, DO wear off when swimming. There are “waterproof” off-the-shelf splints that need to be taken off and blown dried for a few hours, if they get wet. And, there are “waterproof casts”, that hold water like a bucket. It is true that the material in these casts do not actually absorb water. But, the cast itself is a container, into which air cannot easily penetrate. So, moisture is trapped, as well as all the things that water can bring with it — chlorine, dirt, bacteria, etc. So, while technically, “waterproof cast” may be an applicable label, these casts do not offer any more protection from water, and adaptability to water-based activities, than old-fashioned, plaster casts.
These devices are truly water safe. They are made from 100% ABS plastic (the same plastic as in Legos™.) And, not only is the material waterproof, but since these custom-made devices are constructed out of a high-tech, open, breathable, yet supportive, webbing, any moisture that gets against the skin, is easily and quickly evaporated. And, if the water (or sweat) brings along any of its pals, like mud, chlorine, salt, or whatever, you can just take a shower like normal, and air dry! Voila, waterproof casts.