I had been using Kalita coffee basket type filters for a couple of years, thinking that they were manufactured in Japan, an usually reliable country. I thought I had to trust the quality of the product.
Two weeks ago, I was due for reordering 150 such filters from Amazon, when I found out by reading more about them,, that they were not made from paper but from polypropylene, a plastic. I discarded the several ones which I had left, and went purchasing real paper Melitta filters.