I scrounged some floor scrubber pads from our cleaners. They are maybe 20mm thick and 40cm in diameter. The material was quite touch but shows promise. They were unused scrubber pads by the way, used ones would be . . . unpleasant. I pulled at the hedge section with a pair of pliers and hagged bits out of it to make it more irregular in appearance like the field hedges I am used to. I kept the offcuts of course, they work jolly well glued to the Woodland Scenics tree armatures, I just need to find a suitable glue.
Some of our American cousins mentioned filter material, both furnace and fish tank filter was mentioned on different websites. I must have a look at oven extractor filter material as well though my impression is that it is much softer. One of the websites, URL forgotten I am afraid, basically cut discs of the material and stuck it on tapered dowels to make coniferous trees of some sort, it looked much better than my description implies.