Perlite vs Expanded Perlite or Vermiculite Newbie Forum Discuss Perlite vs Expanded Perlite or Vermiculite in the Good Background Information forums; What is the difference in terms of insulating factor? Most of you out there, I assume, are using expanded Perlite ...

[lwood]

What is the difference in terms of insulating factor? Most of you out there, I assume, are using expanded Perlite or what I know as Vermiculite. Is that a true assumption? Even so, how much insulating factor difference is there in the two. I'm sure people are using both.

[dmun]

Perlite is a naturally occurring mineral that looks like this:

As far as I know it has little or no insulation value.
When crushed and heated, it pops like popcorn and produces the little lightweight white spheres that we are talking about in oven building.
Vermiculite is also a heated mineral, but it's brown in color, and the chunks are cubic instead of spherical.

They both work fine for oven insulation. Outside the US there may be some question of whether vermiculite is asbestos free, as the two minerals can be found in the same formations. For this reason, I'd stick with perlite if you can get it.

[shuboyje]

Expanded Perlite has an R value of about 4 per inch of thickness. Vermiculite has an R value of about 3.4 per inch of thickness. Perlite also tends to be cheaper.

[Neil2]

I found the perlite was more "workable" in terms of screeding and leveling.