What material is used to make these bags? And why is the manufacturer reluctant to say that when advertising?

The manufacturer is prob reluctant to come out and say because the tea bags ARE NOT cotton or some natural fiber. They are cheap plastic! A cup of hot tea starts melting the bag ends into plastic. Not sure about you, but I don’t want to ingest tea fused with who knows what?

What is the maximum ounces that this bag can hold?

I don't know about ounces, but it will hold 3-4 heaping teaspoons of tea. It's great too - if you tie it tight not even the powdery tea leaks out!

Is there glue in the top edge that forms the casing for the string?

No, glue. It has possibly heat welding, mechanical stitching. Very clean and nice, I also use these as spice bags in soups - so I don’t have to fish out the garlic- etc.

From what country are these made?

I believe China. 1st bat h I purchased was great & received in a timely manner. 2nd batch were paper thin, ripped easily & took over a month to receive.