I have also seen it said that most PU foam in mattresses these days is bad and does break down, and that is the reason for the massive number of consumer complaints about sagging problems.

So I made this thread to clarify these points so that my knowledge is correct. 

I'd appreciate if the knowledgable posters could answer these questions:

1. How is good PU foam defined?

2. Is there a tangible way to discern good from bad PU foam in a mattress, prior to buying said mattress?

3. Do any manufacturers still use good PU foam today, or is 100% of the PU foam made today crap?  If 100% is not crap, which manufacturers still use good PU foam?