If your attic currently has vermiculite insulation, you need to be very careful. Vermiculite is a naturally occurring mineral that expands into a lightweight material when heated (kind of like popcorn). Unfortunately, one of the main vermiculite mines in the US until 1990 was found to have a natural asbestos deposit in the same mine, which means vermiculite insulation installed in North America before or during 1990 may be contaminated with asbestos, an extremely toxic fiber. Although this mine was shut down I still don't recommend vermiculite - asbestos might be found in some other vermiculite mine later, and vermiculite has a lower R-value than most other materials.
If you do have vermiculite installed, leave it alone, or hire someone to test it for asbestos contamination before you replace it or even disturb it. If it does contain asbestos it is safe if undisturbed, but to remove it you'll need to hire people who specialize in asbestos removal.
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