I made a home test on the various material for rods last year, or maybe the year before. This subject creeps up at least once a year and there are always people who jump to the protection of fiberglass as being the end-all best material for a rod - becasue that's al they use, or read in Muzzle Blasts it was one of the best.
The lack of knowledge in this subjuect will ruin your barrel. There is fiberglass - bare and MOST abrasive just as many of us have said - believe it - we are not lying. So- why the defenders - COATED fiberglass where the fiberglas never touches the barrel walls is being called a "fiberglass rod", wherein it is not a fiberglass rod, but a coated fiberglass rod. The difference is a ruined barrel in less than 200 shots. Now, 200 shots is more than some members here have fired total, or more than they fire in a year. 200 shots is not very good mileage for a $100.00 to $300.00 barrel + costs of installing and finishing.
In my tests, Hickory and nylon were the least abrasive doing little more than wearing off the bluing on the piece of 12L14 I used for the test. Stainless steel was second to fiberglass, then tool steel ie: commercial drill rod, then aluminum, then nylon then hockory.
Differing hardness of barrels steel might also produce different results, but I'd think, only in severity, not in order of abrasiveness.