Couch: Stressless foam density?

Hi all, looking at a new couch because our previous one (Living Spaces, foam density 1.8lbs/feet^3) has completely collapsed.

After reading 23424 posts here one of the brands that stood out was Stressless.

However, when reading about their foam density, it's now 30kg/m^3 which ends up at ... 1.8lbs/feet^3: https://bascdn.bscdn.info/bcimages/_PDF/Stressless_Emily_Technical_Specification.pdf search for 'foam density'.

That seems to be low according to this [reddit post].(https://old.reddit.com/r/BuyItForLife/comments/1bglyfz/bifl_furniture_recs_specifically_couches/kv85zpv/)

So what gives? How is the Stressless so much better vs other brands? What am I not seeing?