OtherMikey. The only cartridge I use a filler in (Cream of Wheat) is the 45-70. I don't think fillers in handgun rounds is a good idea. There was a sidebar in an American Rifleman about a guy who was having problems using dacron as a filler for light loads in his .44 Mag. Seems the stuff was melting and gumming up his action and barrel. The answer was find some kapok. Not in this day and age.
I had about 30 pounds of kapok from an old mattress, but it got lost somehow in the move to AZ. Dang it all.
Anyway, I have never seen the need for fillers. I just use a powder such as Bullseye, Unique, and I'm starting to play with W-231. They should work for light loads.