Nothing specific. Most everything printed that I have since circa 1980s is fine. I expect looking after them matters more than paper quality.

Thats mostly paperback novels.

Stuff that was printed cheap in the 30s and 40s (ie "pulp" fiction) is taking strain now - which is to be expected.

Books I got as a child seem yo be I fine condition, despite a lot of rough handling at my hands, and my kids hands.