The West 410 is a fairing compound and is not intended as a structural filler. The 407 Low Density Filler is primarily the glass bubbles with a few other additives. Being a cheapskate, I would just get the glass bubbles and maybe add a little coloidal silica.

> West System 410 Microlight is probably the lightest.

> A much cheaper alternative though (and a close second in weight.) is 3M
> K15 Glass Bubbles.