Alumina Trihydrate (ATH)

It is a flame retardant mineral filler. Added to resin, gelcoat, or casting compounds it improves fire and smoke resistance and adds body. It is also used as a smooth, sandable filler and in casting and solid surface work.

When heated it releases water and absorbs heat, which slows ignition and reduces smoke. The more ATH in the mix, the greater the effect.

ATH mixes into epoxy, polyester, and vinyl ester resin. It is a mineral filler used mainly for flame resistance and for a hard, dense, smooth fill. Add it to mixed resin to the body you need. Because it is denser than glass fillers, use it where fire resistance or a hard surface matters more than weight.

Yes. ATH makes a dense but workable filler with good sanding characteristics, harder than a lightweight fairing mix but still fair-able. It is the better choice where you want a tough, smooth surface rather than minimum weight. For large fairing jobs, a glass-bubble filler sands lighter.

ATH is a higher-density mineral filler, so it adds more weight than glass-bubble fillers like microballoons or Q-cells. Use it where flame resistance or a hard, smooth fill matters more than weight, and choose a lightweight filler when keeping weight down is the priority.