http://www.westsystem.com/ss/product-selection-chart/

I believe all the bondo type products are polyester resin. At least they used to be. Polyester can be thickened with cab-o-sil which I think is collodial silica.

The traditional problem with bondo is that it started out using talc as a thickener which led to water absorbancy problems.

Newer products, particularly those described as lite, may not be so prone to absorbancy.

I've been using a lite body filler on my Blade for some time and have had no problems.