The lake John White explained it to me pretty well. Plain 105/205, 206 or 207 is basically laminating goop. You make fiberglass out of it. 207 is the clear stuff. If you want to use it for adhesive or filler, then you add the other stuff to it. He told me to use colloidal silica. The other popular option are the micro bubble spheres or whatever they are calledPrice wise the 105/206 is a better buy with no filler. does the filler make that a better bond?