3M Microballoons

These microscopic glass spheres added to resin systems make a lightweight, easy-to-sand putty for minor surface filling of cracks, holes, etc.

Used in lower concentrations, they “extend” resin by fluffing it up and reduce shrinkage, they also have very good compressive strength. They differ from “Q-Cell” in that microballoons are more consistent in size. This is better for a variety of reasons.
(Color: White)