Adding both milled fiber and cabosil: The cabosil keeps the mixture from sagging, without it if placed on a vertical surface it would most likely run. Of the three fillers I use, milled fiber is the heaviest, then cabosil and then Micro balloons. The strength profile is in the same order. The filler choice is dependent on the strength required. Most times it is cabosil and milled fiber just like this picture of a landing gear plate being bonded into a fiberglass fuselage. As far as weight is concerned, using the method gives me a slight weight reduction due to being able to use less adhesive then if I were to use straight 1:1 " minute epoxy ".
