These brushes are so necessary to fiberglass work that we have spent considerable effort in finding the best source. Constructed of pure china bristle for the stiffness required to stipple resins into mats and fabrics. Epoxy potted bristles resistant to all solvents. Sanded wood handle for ease of grip and solvent resistance. We do not recommend these brushes for finish coats as they tend to leave bristles which are otherwise harmless in laminations. These brushes are all 1-3/4" trim length and 5/16" thick.