# What is the fabric in heating mantles made of?

An ordinary lab heating mantle often has a white fabric coating for the flask compartment, which looks like an inorganic fiber:

Image source

I'm pretty sure that for some time in the past asbestos was used for that; these days I think it's some kind of woven fiberglass (assuming the heating element produces elevated temperatures up to about $\pu{400^\circ C}$), but I'm having hard times finding an exact chemical composition.

Also, what kind of chemicals can react with this coating? I guess something like molten $\ce{NaOH}$ and the melts of alkali metals can cause some damage, but I'm not sure.

• Those older ones are often made of woven fibreglass, traditionally with aspestos behind, or nowadays usually some sort of ceramic. More modern isomantles use an aluminium mesh instead of the fabric, again,with a ceramic insulator behind. – NotEvans. Jul 30 '17 at 7:47