One of the builds I would like to do at some point is a mermaid tail. One of the ideas I have had is to have a smooth transition/blending edge between the fish tail and the human skin of the wearer. While this could be achieved with traditional make-up techniques and airbrushing. A transparent rubber area around the hips would work well. The color of the fish skin could become less and less opaque, allowing the natural skin color of the model to show through.
Does such a thing exist? I've used many of Smooth-On's products but they are mostly a water white translucency. They have some rubber glass that is a platinum cure silicone, but these are designed for break-away glass effects and have low tear strength. There is Solaris but still not that strong and I don't think it is skin rated.
There are urethane rubbers out there but I am not that familiar with them other than using Smooth-On's Brush-On 40 as a paint base for painting flexible foam pieces.
I came across a kind of crafty sort of product that involved rubber pellets I think and had a lot of interesting properties. It melted down with a heat gun or something and you could add stuff to change various properties, but I haven't been able to locate it again.