100 years ago, asbestos was the new wonder material, and "We added asbestos to stuff" was a very common marketing bullet point for building materials. It found its way into flooring, mastic, the predecessors to drywall, ceiling texture, insulation, and anything and everything used near a combustion appliance.
Literally just, take a process that used to use sand or horsehair or whatever filler, and add a significant portion by mass of asbestos powder instead.
It's also still used in building materials in developing countries, it's an incredible material that happens to give people cancer, mainly workers.
The R-value performance numbers for asbestos as building insulation are wildly divergent, but most of them aren't especially competitive with modern materials.
I'm not sure how to square that with claims like:
> With phenolic resins, asbestos products are produced which will provide insulation and retain strength when subjected to 5,000°F for periods of minutes (1 to 30 minutes) . See Figure 2.1 in which a rocket motor part is subjected to a temperature of 5,000°F. Figure 2.1. Rocket motor aft (asbestos-phenolic insulator) before and after firing at 5,000°F.
> The temperature approximately 1/8 in. from the surface exposed to 5,000°F will be approximately 200°F after 1/2 to 1 min. of exposure.
> When combined with magnesium carbonate and other similar products, heat insulators can be produced which will be useful for many years in such applications as boilers operating at temperatures from 500° to 1,200°F or 1,800°F.
We seem to use a matted "Ceramic Fiber" roll for its high-heat insulation capabilities these days, up to about 2300F-2600F depending on type. Asbestos fiber insulation seems to be good to somewhere between 1500F to 2700F depending on how you use it. Ceramic fiber is carcinogenic in a similar way to asbestos, but apparently considerably safer due to the fiber length/alignment.
I wonder if there are studies on the lives saved by asbestos's fireproofing feature vs. cost by its lung-disease-causing feature.
Answering my own question: the WHO estimates it costs 200K lives per year. No estimates on the other side, but that's a big number to overcome...
https://www.who.int/news-room/fact-sheets/detail/asbestos