403 Microfibers Adhesive Filler is a fine fiber blend. Use it to thicken epoxy blended resin/hardener and create a multi-purpose adhesive. Itâ€™s most popular use is for bonding wood. Epoxy thickened with microfibers has good gap-filling qualities but will still do an excellent job of wetting-out/penetrating into wood fibers. 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, it will cure to an off-white color.