FGCI is a very 'down home' kind of business, call them up and just ask for the catalogue saying you saw it in WoodenBoat mag and they will send you one free. A very informative document it is with lots of 'how to' in it.

Milled fiber is always cotton to me , at least that is what I always get when I order it . Glass powder is another thing you want to be careful with .

Say your epoxy was a 1000 gal batch, and you had the choice of thickening with 3x5 notepad paper or 1' long pieces of rope .
Which would be stronger?
The notepad paper would be harder as it absorbs the epoxy , but the rope will be stronger because it mats and meshes together to form a interlocked structure .
Anywhere you want to bond surfaces and one can absorb any epoxy mix , fiber is better because on a microscopic level the fibers are drawn into the material , such as wood or foam. With cabosil the epoxy is drawn in and the silica stays out weakening the epoxy ( starving the joint ).
Cabosil is an excellent product and makes a very hard , extremely hard epoxy.
What most people don't realize is, your epoxy additives are like spices , most of the time you need more than one in the soup .
Say you are mounting deck hardware with 1/4" screws , drill a 3/4" hole fill with cabosil epoxy mix then drill a 1/4" hole in the center of that . That is what silica is good at .
Laminating a new mast step , 1/2 cotton & half silica in a loose mix more like puddin then P-nut butter and dont over clamp and squeeze it all out .
Fixing dings , use Barney Dust ( micro spheres ) with a dash of cotton and silica ( silica sands very bad so you need a softer filler).

Ok now , for more secrets you'll have to buy my new DVD "Epoxy Tips" for 29.95 + S&H ( west coast add $100) allow 6 to 8 months for delivery.