Fairing compounds or putties typically contain the following:

1. A resin such as epoxy, polyester, or vinyl ester
2. A hardener (for epoxy) or catalyst (for polyester/vinyl ester) for activating the resin and ensuring that it eventually cures to a hard, plastic material. Always use the exact amounts of hardener or catalyst specified by the manufacturer, or the resin will not cure properly.
3. A low-density filler such as fumed silica (epoxy) or chopped fiber (fiberglass strands) (polyester/vinyl ester) for thickening the putty so it won’t run or sag
4. An additive (such as glass microballoons) that makes the compound easier to sand after curing, since the resin and thickening agent alone result in a cured substance which is very hard to sand smooth

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