does it really matter which one is used? what is the difference?
Each will give you a slightly different outcome or finished product
It is best to experiment and see for yourself how the pieces differ.
For me, it seems that the hypertufa made with vermiculite has a slightly different texture when mixing, almost like it stick together better.
When the containers are curing and you rough up the sides with a steel brush the exposed pieces of perlite makes the piece look like granite. The vermiculite looks a little shinny.
Sometimes I use both.
I found that using vermiculite makes a denser mixture and you will need more to make a trough, thus the trough is heavier; it is much finer than perlite. Depends on what you prefer. I like them both, but use perlite to get more volume per batch. Sometimes I throw some vermiculite in just for occasional sparkle.
thanks to both of you for the information