Efficient Solar Water Still - novel design using a floating element that wicks the water

I thought folks might like this article on a solar still for water purification that's a somewhat different take than others I've seen. It seems like a good starting point for variations. The idea is to use sunlight more efficiently by insulating the water and only heating up the water that's being wicked into the paper. They have another picture in the article where they're floating the still in a body of water.

http://www.sciencemag.org/news/2017/02/sunlight-powered-purifier-could-clean-water-impoverished

Does anyone have ideas for replacing the polystyrene insulation? Cork maybe? Ideally it would be something that floats. Alternatively, reusing/recycling polystyrene might work. I also thought char cloth could replace the carbon coated paper, but I don't know if that would be an improvement or not.