Repair fiberglass(?) pack on top of front fender liner?

Above the wheel on an OEM front fender liner there is some white fiberglass (I think) material with a sort of fabric top layer to keep it in place. The original liner for my car had a hole punched through it down low, not near this padding, and it was replaced with an aftermarket liner, with none of this fibrous material, but the fit was not great:

Replaced fender liner, so so fit | PriusChat

So I think I will patch the hole in the original liner and put it back on. My caliper showed the thickness in that region to be .04 to .05 inches, and online one can find small sheets of .04 inch ABS for less than $10. It is ABS, yes? The replacement part's material is just described as "plastic". Could be something besides ABS I suppose, like HDPE or vinyl.

Anyway, that fiberglass, or whatever it is, on the old one is turning to powder. For all I know that may just be age, and it might also be the case on the passenger's side. I'm not pulling that one off to find out. If I pick up the one which is off the car all sorts of dust/fibers float out of that section. Doesn't seem like a good idea to put the part back on while it is emitting clouds of mystery dust/fibers. I'm thinking scrape the disintegrating material off (with a respirator while sucking up the crud a shop vac with a HEPA filter). Glue some new fiberglass (?) on to replace it? Or not worth the trouble to replace the fibrous material? I'm leaning towards "not worth the trouble", but fiberglass in various thicknesses is easy to come by.

 

Found one material that appears to be for the same purpose - Resonix Fiber mat. Look down about 2/3rds of the way towards the bottom of this link to see a picture of them glued on the top surface of a wheel well liner:

Reduce Road & Tire Noise With Wheel Well Sound Deadening Treatments - ResoNix Sound Solutions - Premium Automotive Sound Deadening Materials

Kind of expensive though.