Green Roof filter material prevents a drain core to filling with debris, and inevitably reducing drainage capacity or even drain failure.
A non-woven filter fabric, most like the fabric you can buy at a local hardware store as a weed barrier for your garden beds, is often used.
These Non-woven fabrics are produced by spraying tiny strands of material over one another. They are not the strongest material and have been reported to be susceptible to clogging because of the non-uniform spacing of fibers.
Woven fabrics allow the passage of fine silt particles, which can flow out of the drain core with the water with drain water, thy will not trap these particles, as can happen with non-woven fabrics..
We would highly recommend to read this educational article on the subject
Regardless of your situation, a drain core should be protected against debris, and one of the two filter materials would be the preferred choice.
We can guide you to the material that is best for your specific Green Roof.