Ummm, the new generation are made out of hard glass rated with 9H hardness. They also (the newer generation glass protectors) are compatible with the new 3D Touch feature of the 6S.I'm curious to know what the "feel" of these protectors is like. Two years ago I decided to go sans protector and haven't looked back. Sure you get some scratches here and there but the feel of the screen is so much nicer.
So it's GLASS, and it feels like the glass that's built into your iPhone.
All of the "anti screen protectors" people are probably criticizing those flimsy PLASTIC screen protectors that were the norm 3 years ago. The newer glass ones have taken over as the new standard.