8mm Dense Spring Tufts from the Diorama Series.
 
These tufts have an adhesive backing, but for extra security add a little PVA before sticking them to your bases.
 
Tweezers are your friend.
 
Note: The blister pack label states that these are 6mm, but they were printed incorrectly. The SKU code is correct 8130, meaning they are 8mm tufts, I also checked them for size.