Originally Posted by Adlerdriver

The 787 carbon fiber fuselage allows Boeing to pressurize the aircraft to a lower cabin altitude than a similar aluminum design. Since that aircraft also uses an electrical pneumatic system rather than the traditional bleed air system on most aircraft, they can accomplish this increased pressurization with no additional demands on the engines. Nothing come for free, so I would imagine the electrical demands are considerably higher. This may demand more from engine driven electrical components but obviously that was deemed to be an acceptable tradeoff by the designers. From what I understand, in actual practice, this electric-centered aircraft design has had some growing pains in terms of system reliability.

Cabin pressurization is a fairly simple concept and the physics involved with actually accomplishing it aren't going to change. You have to pump enough air into the fuselage to sustain life inside a tube that spends hours above 30,000 feet. It seems like Boeing was able to make some minor "breakthroughs" in fuselage structure and system architecture that allow them to get cabin altitude lower without major sacrifices in efficiency. They were able to drop it from typical ranges of 6000-7000 feet down to 5000-6000.