Cob: RE: Insulation - vermiculite

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 per·lite also pearl·ite n. A natural volcanic glass similar to obsidian but 
having distinctive concentric cracks and a relatively high water content. In 
a fluffy heat-expanded form perlite is used as a lightweight aggregate, in 
fire-resistant insulation, and in soil for potted plants. [French (from 
perle, pearl, from Old French; see PEARL1) or German Perlite (from Perle, 
pearl, ultimately from Vulgar Latin *pernula).] --per·lit“ic (p
r-l¹t“¹k) adj.


 ver·mic·u·lite n. Any of a group of micaceous hydrated silicate minerals 
related to the chlorites and used in heat-expanded form as insulation and as 
a planting medium. [Latin vermiculus, diminutive of vermis, worm; see 
VERMICULAR + -ite1.]