"HTH" wrote in message
...
I think what Ingrid is talking about is the stuff I was looking for.
The problem is I was looking at the home centers and it lives at Wally WORLD.

It is not the common blue fiberglass filters that most furnaces use.
It is a much heavier and perhaps more open matt. The fibers are encased in a
fiberglass net with about 1/4 inch between threads.

It is faily good a pick up larger particles and extends the life of the
poly batting that I use under it.

HTH

Here is an interesting article on filtration, if you are interested.

http://www.akca.org/library/trickle.htm

I use open pore polyester foam (about 1/3 inch in thickness) as a mechanical
filter in my prefilter. It works well, and with my biological filter working
properly, I don't have to clean it very often.