I wish that I new and could be more helpful. I can not picture the insulation that you are working with.
My advice is to treat it as suspect and have it tested. It sounds that it may be friable if it is asbestos, as such I would get it tested (or verify that it was previously tested and found free of asbestos) before working near it. It very well may be worth the delay.
I am sorry that I do not know enough to give you a correct answer. It may help someone else get you the correct answer if you could post any identifiable marks or even a picture or two of the stuff.
