Ever heard of felt shed?
The fibers that are woven to make felt shed.
used to manufacture the Felt may be incorrect either for the application or for Felt manufacturing. Obviously, certain fibers withstand certain elements that others will not. One fiber type may perform exceptionally well at 175° C (347° F), while another becomes brittle, breaks, and sheds. Or, certain finishes, like silicone, may have been used on the fiber allowing it to be too slippery and shed. Another consideration may be the length of the fiber staple - too short and it resists proper locking during the needling process.
Saving a few bucks will cost you in the long run. Felt is not used to make air filters.