Ah, I can see the source of the confusion here. Two different cart
mods have melded together in your mind.
BFM, Blue Foam
mod, uses blue foam which is Marineland Rite-Size U bonded foam sleeve.
Fluval is white and is called Fluval Water Polishing Pad which is a different way of getting filler for carts.
Now that we have the two separated, don't forget to rinse your choice out real well before you start. I like to use grain alcohol, Everclear or PGA, when I clean them for the first time.