The name Gilsulate® was first trademarked in 1943.  The product has evolved over the past 60+ years. The original product was a specific mineral called Gilsonite.  It was a black bitumen type product and came in three grades, A, B and C.  This formulation remained unchanged until the early 1970's.  Product formulations and particle engineering greatly improved the product in the late 1970's into the patented formulation that  remains unchanged today.  

In the text boxes to the right and left are logo's for Gilsulate insulation, not their manufacturers,  over the years.