I’ve seen stuff like this – they sell it in craft stores. I noticed it when it was used as a votive candle centerpiece at a wedding I attended; the powder was added to a clear bowl, and once water was added in turned into a gelatin-like substance, on top of which was floated a few votive candles. It was actually kinda neat.
There are several non-gelatine powders that turn water into “goo”. One of them is polyoxymethylene (POM). They probably aren’t using that, since I can state from experience that getting it to mix without clumping is a bitch. But it is nontoxic.
I bought my wife some of that stuff for her last birthday.
It’s pretty neat- once it’s all dissolved, it’s a uniform watery gel. It holds heat really well, so you have to make sure you don’t make the water too hot, or you’ll scald yourself.
When you’re done, just pour in some salt and it all liquefies so you can drain the tub.
My dad used to work for J&J, in the non-wovens and superabsorbents department (that is, he designed diapers and maxi-pads and the production lines to make them. Try sharing that with the class in fifth grade.) When I was in junior high, the very first superabsorbent diapers were coming out, and he helped me design an experiment for the science fair comparing traditional wood pulp to superabsorbents. He snagged a bag of the superabsorbent powder for me from work - long before it was sold in gardening supply stores. As part of my project, I mixed the powder in some water for a demonstration, and took first place and went to state (I think I got third there. Product comparisons don’t do well at state.)
I have no idea why you’d want to bathe in it. I did always wonder what a whole grocery bag full of it would do to the neighbor’s swimming pool, though.
Do the people across the pond really call a “bath” a “baff” or I am just not used to the accent?
As a related anecdote.
My dad, for some unknown reason to me, has always had a hard time pronouncing the “th” sounds at the end of words, but not at the beginning of words, and he would call a “bath” a “baff”.