Not completely interchangeable. For one thing cel-o-fil cures to a cream like color where the wood flour is a dark brown. With a bright finished boat this will be noticeable. I speak from experiance. WEST fillers are not the same color or shade as MAS.

Also, they are different textures to suit thier different uses. The wood flour is course and bulky to increase the volume and decrease the wieght of the epoxy for use in fillets. The cell-o-fil is fine and gritty to hold the epoxy in place when bonding two surfaces. You can form a fillet with the squeeze out of cell-o-fil but get it right before it sets because it's a bugger to sand. I wouldn't use the flour in place of cell-o-fil when bonding. I don't think it would be as strong as with the cell-o-fil.

FY I - I've used nothing but woodflour and never had a joint fail, Relative strength is not an issue, Both fillers make joints that are stronger than the wood.

Laszlo

  geotx,

  Mixing the two can result in a better looking fillet too. The two fillers by themselves  sometimes 'clash' with wood that will be finished/bright. Experiment a little and you can find shades that blend well with the material being bonded.