I have a house that was originally built in Chicago in 1954 that had an addition put on in the 90's. The original roof and part of the original exterior was built over is now visible in the attic of the addition. This is a picture looking at the back of one of the original walls, it may have been an exterior wall. I'm not sure if this was sheathing or insulation. Notice there are white strings running through the material and it's uneven, almost like tree bark. The gray on the right of the photo is the exterior, which is brick.

Any idea what this material is?

wall material

  • Possibly glass fibre plus crap.
    – Solar Mike
    Sep 13, 2020 at 5:35
  • And fiber glass is very similar to "rock wool" . It is nasty to handle ,gloves needed to handle either to avoid irritation. Modern fiberglas is much easier to handle. Oct 19, 2020 at 2:07

1 Answer 1


Finally figured it out after having found another location that was more accessible with the same material. It's Kimsul balsam insulation.

Kimsul Insulation 1 Kimsul Insulation 2

  • 1
    Thanks for coming back to post your answer; you can choose it as "the" answer by clicking the checkmark. And, you should probably take our tour so you'll know how best to contribute here. Oct 18, 2020 at 22:40

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