In my attic, I have found two types of blown in and/or loose fill shredded insulation, in two layers, totaling 6 inches of depth. The bottom layer is a very dark gray wool, where the top layer is a yellow shredded material that I think is fiberglass. The house was built around 1950. I have been laying blankets of fiberglass insulation to increase the R-value, but I was concerned there might be asbestos. What are the two layers, especially the dark gray one? Rock wool?
The darker one is most-likely rock wool with a mixture of vermiculite.
Sounds like rock-wool, I have it in my 1950's attic too. FYI: asbestos insulation is an off white color and about the only place you find it in older homes is wrapped around steam pipes and old boilers.
