What is this insulation?

[Peter Louis]

Built in 1970. this brown stuff at the bottom of attic insulation; the cellulose & fiberglass added on top, no vapor barrier found.

What is this? Thank you.

[John Kogel]

Wood fibre insulation.
It is treated with a fire retardant and maybe a dye that gives it that colour. I have tried to burn it, 50 years old, no way.
I normally would not see it in a 70's house, usually much older houses.

[Peter Louis]

Thank you John