3M Glass Bubbles, 10 lb. Box
Hollow glass microspheres, use to extend resin, to reduce weight, shrinkage and sanding effort.
Commonly used to make lightweight fairing compounds or putty for ding repair, also known as Q-cil. Can also be used to make tooling paste or cast parts.
A basic putty recipe is:
1 part resin by volume to 1 part 3M bubbles by volume - add cabosil to get desired thickness
The 3M Bubbles will extend and thicken the resin to a degree, but it is a bunch of marbles in solution so it will want to run and level out, adding cabosil will allow you to make a paste that you can stick on a wall or ceiling (if so desired) and won't affect the ability to sand the cured putty.