Insulation and razor blades

Putting up insulation for the first time in my life, and noticed that my razors get black crap all over them in short order.
Is the fiberglass doing that, or is it some glue in the kraft paper?
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The paper is coated with tar as a vapor retardant. Also doubles as the adhesive that holds the glass on.
TAB Dude
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Yes, that is adhesive and moisture barrier, the goop, that is. I find it much easier to use a very large pair of shop scissors to cut the batts in two stages, first on the paper side, then the pink fuzzy side, and it comes apart. Also, much less buildup of tar vs a utility knife blade.

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