This is basically a rephrase of this question from Sustainability SE. Paper manufacturer UPM claims they have paper that has the same key characteristics (as white, as thick and as usable in office equipment) as "usual" office paper but lower "grammage" (mass per square meter) and therefore (the claim continues) lower load on the environment.
One example is UPM Kymmene Yes Paper - they offer Yes Light with 70 gsm grammage and Yes Bronze copy/print with 80 gsm grammage. Looks like the two papers are very similar in everything except grammage and brightness (and 70 gsm paper even has better whiteness):
Grammage Thickness Opacity CIE Whiteness Yes Light 70 gsm 0,105 mm 92% 165% Yes Bronze 80 gsm 0,104 mm 93% 150%
the manufactures further says that 70 gsm paper has 10 % smaller environmental load per sheet compared to the same paper in 80 gsm.
They claim 10% lower load, but 70 gsm paper uses about 12,5% less abstract "material" compared to 80 gsm paper. Where have the 2,5% disappeared? It's "just" 2,5% when you compare 2,5% and 100%, but it's 20% difference when you compare 12,5% and 10%. If the process was explained - something like well, we make tiny enclosed pores in the sheet and that allows us to use 12,5% less fiber, but we need more energy for making those pores with compressed air so we lose those 2,5% for making pores and so the net advantage is 10%. And btw here's how we estimated that the extra energy we spend amounts to about 2,5% and not any other number. Nothing like that. The process is not detailed and there's this "10%" claim out of nowhere.
So the manufacturing process is not detailed. Do they use less fiber? How do they achieve the same thickness (do they use or add plutonium or other not so green materials)? Finally, if there exists such a brilliant technology for producing paper as usable as usual one but with less raw materials why wouldn't everyone license it?
So my question is...
Is there any independent data on how such paper is produced and how its manufacturing process is different from that of "usual" paper in environmental terms?