What kind of insulation is this

[JORY LANNES]

This is insulation installed on a cathedral ceiling built in 1957. Can any one identify what it is and is it safe.

[Cary Seidner]

Jory,

That is a Tectum panel. It's a deck substrate.

[Jerry Peck]

That is Tectum roof sheathing which served as thermal insulation, roof sheathing, and acoustical insulation all in one.

Rare to find it in houses, but I have a few times.