even the "isolation" of the dome is exclusively lightweight concrete (vermiculite/perlite-portland cement ca.5:1)
I know there are some discussions about, but the neapolitan not make it otherwise... on the contrary, they use the cheaper (but much heavier) leca balls instead of the vermiculite/pelite.
I do not want to say that it is the best solution, but it works great!
the oven is barely warm to the outside but keeps the heat inside on days.
you live not 10 minutes away, come and see for yourself.