The video doesn't explain what the material actually is. I thought it was hot wax at first, but it seems to sit around too long. Is it reacting with the water? (is that big bowl even water?)
I think the colored wax buckets were sitting in a tray full of warm water. Maybe even with the small warming burners underneath like how catering folks do it.
Wax would melt or sag though, and that would be an issue if these are intended for window displays. There's also a bit in the original video where he puts one in the oven to cure some additional material (which looked a bit like PVA).