Insulbrick is a fibreboard sheathing coated with tar and added granular material, similar to asphalt shingles. The surface was stamped with a brick or rectangular stone pattern. Insulbrick is a brand name and was used for all types of asphalt siding much like most tissues are called Kleenex.
I remember that product, it was a hardboard material and was made to imitate brick, stucco, etc., and was a similar material to Masonite siding. It could have been manufactured by Masonite or Abitibi or another.
Can’t find it online, but I used to see that in the early '70s.