Paper mill felts or paper mill wires are wear parts on paper machines that are usually utilized at the start of the papermaking process to assist in dewatering stock as it is initially formed into a sheet. You may find felts all along a paper machine to help guide and dewater the sheet.
People that I know utilize it for pathways that need to be able to drain water but to keep down weeds.
Modern felts/wires are made with synthetic materials. Ones that are being disposed of may have rips, tears, or have clogged pores due to use.
Personally, I would not recommend utilize them because you do not know what materials/chemicals have been utilized in the paper making process that might still be on the material.