Flotrex filters use a pleated microfiber filtration media, while the Memtrex series use polymer membrane filtration media. As such, the Flotrex filters are more economical, but the Memtrex filters have lower micron ratings and sharper retentions than the Flotrex filters. Memtrex filters are typically used as the final filtration step, while the Flotrex may be used as a prefilter or final filter in some applications.