What is the caulking around the window? ?

[total]

Replaced a window today and encountered a new material for me. Does anyone know?

It was used as packing (insulation) around a window that was installed in the 60s.

Looks like hair (?) smells like tar and seems to be burnt. The burnt marks are also visible on the leca stones as soot where the strip was attached.

 

[tergo]

probably tjärdrev
https://www.byggnadsvardsbutiken.se/product/tjardrev

 

[total]

probably tjärdrev
[link]

Saw that too, but I don't think it's lin.
Could it be tagel?

 

[Teakster]

It's probably horsehair or cow hair - was common for caulking windows.