"407 Low-Density is a blended microballoon-based fairing filler for WEST SYSTEM Epoxy. Add 407 to a mixture of epoxy resin/hardener to create a fairing putty. It’s easy to sand or carve this putty once it has cured. The filler is reasonably strong on a strength-to-weight basis. You can blend it into any WEST SYSTEM 105 Resin/20X Hardener combination, G/flex Epoxy 650, or G/5 Five-Minute Adhesive. Blended with epoxy to a “peanut butter” consistency, it will be easy to fair. The higher the percentage of 407 in your epoxy mix, the easier it will be to fair. Cures to a dark red/brown color.:"