Generally, the Airbus A350 is considered significantly more comfortable than the older A330 due to its "next-generation" cabin technology. As a "clean-sheet" design made largely of carbon-fiber composites, the A350 allows for a lower cabin altitude (making the air feel more like you are at 6,000 feet rather than 8,000) and higher humidity levels, which greatly reduces the physical fatigue, headaches, and dry skin associated with long-haul flying. The A350 also features a wider fuselage, which typically allows for wider seats in Economy (18 inches compared to the 17 inches often found on the A330) and more "vertical" sidewalls, providing more shoulder room. Its advanced LED lighting systems are designed to mimic natural circadian rhythms to help reduce jet lag. While the A330neo has updated some of these features, the A350 remains the "gold standard" for passenger comfort on ultra-long-haul routes, offering a much quieter engine noise profile and a more spacious, "airy" cabin feel that is immediately noticeable upon boarding.