I have a bunch of textiles here as well as different fibers , felts, suedes, wovens, non-wovens, knitted, you name it.
I have tried different foams (also reticulated foam), high density visco elastic foam etc....
Today i made a mistake and ordered a fluval bag.
It's a thin absorbent net that is used for containing the filter media.
Liquid really flows
through it nicely.
It's working the best of everything i have ever tried. (much better than the fluval fluff)
Foam is too absorbent and will keep the liquid inside.
Felt, is actually a woven polyester, you may as well use a cotton cloth or T shirt material.
The net i'm taking about, can be washed and it's like new...you don't need more than one little piece bunched up.
Keep in mind that the net is polyethylene. It will melt and burn like polyester.
So use at your own risk.
I think all these materials would be appropriate if there were a small spring creating an upward force, that continuously squeezes the juices onto the atty.
One guy wrote about surrounding the spring with filler material.
I suggest placing the spring under the filler material so it presses up vertically onto said filler material.
Here is a pic of that net...I know it looks weird, but i have not found anything better to date.
The net is sort of springy itself, this is why it may be working so well.
In other words, this fluval net net has an upward spring effect when compressed downwards into the cart.
Try it, you will not regret!!