With the job of the inner dome being to soak up heat, the job of the insulation is to retain the heat within this inner layer. By retaining the heat it increases cooking temperatures and duration but also protects the outer decorative and shaping layers of the dome from the intense heat (i.e. it stops the outside of the oven getting too hot).
This insulation layer is usually a ceramic fiber blanket as it is convenient and has excellent thermal resistance at high temperatures (i.e. it insulates really well!).
Other insulating products such as perlite, vermiculite, rockwool and pumice can be used but they need to be applied in a thicker layer than ceramic blanket to achieve the same level of insulation. Being in concrete format, they do not provide flexibility for the inner dome expanding during heating so cracking can occur.
Glass wool or fiberglass insulation is not recommended as the binders (glues) used to hold this material together cannot withstand the high temperatures. It's just not designed for the application.
Ceramic fibre insulation (pic 1 & 2) and perlite set in refractory cement
See our range of insulation here
