Type of Attic Insulation?

Apologies upfront if I am a dork that can’t identify a common insulation material. Standard 1965 stick-built, single family, detached house. The top (second) layer is definitely blown-in rock wool. What is the fuzzy yellow-green insulation layer underneath?

It is definitely not vermiculite. Thinking it might be cellulose with some type of fire-retardant treatment(?)

1 Like

Balsam Wool by the looks of it.
How to identify insulation
Balsam wool insulating blanket used wood fibers from tree bark, wood pulp, or other lumber byproducts. As such it is a wood or cellulose product and not an asbestos-containing material.

Watch out: however, from 1958 through 1974 asbestos was used in the production of other products at the Conwed Corporation (Wood Conversion Company) plant in Cloquet, Minnesota, including the production of ceiling tiles and other products.

1 Like

From here, it looks like some mineral wool on top of cellulose.

1 Like

Looks like blown pink fiberglass over old blown cellulose.


I agree with Randy. The top layer looks like common blown-in Owens Corning (Pink Panther) fiberglass has been added over the original darker colored and denser insulation.
I’m not sure about the original insulation. From this picture I would think either cellulose or rockwool.
Did you feel it? Rock wool feels very different than cellulose.
The lick test is tried and true, but I hear that test is being retired.


I’ll put 50 on rockwool :grinning:

1 Like

Thanks guys. The second bottom layer had a fuzzy feel (like an organic sponge or cotton ball) and looked like it had saw dust infused into it, including tiny bits of wood. I have read in Robert’s link that they used to infuse sawdust into cellulose products back in the day. So, my money is on cellulose for the bottom layer and it was yellow/green due to the color of the sawdust, chemical treatment(s), age, or some combination thereof.

1 Like

Thats true!!