NRR provides a specific method for testing a headset's noise attenuation over a wide frequency spectrum, weighting the various frequencies, and arriving at an overall rating in decibels. In-flight impressions earcup earseal headband microphone and boom My subjective reaction while flying with the QFR Solo bears out these numbers. I found it much, much quieter than the H10-13.4, and also more comfortable to wear. The 20XL reduces engine noise a bit better, but the QFR Solo reduces wind noise better. I found the new QFR Solo passive to be very nearly as good, and in some ways better.
Comfort is even more subjective than quiet.
My co-pilot did not. Obviously, either our glasses were slightly different, our head shapes and skull structures were slightly different, or both. Whatever the exact difference, this underscores my often-repeated advice that no matter how many specs and review articles you read, there's no substitute for actually evaluating a headset in the aircraft. Most reputable dealers offer a 30-day return privilege, giving you an opportunity to try the thing in flight, and I suggest not purchasing from any dealer who doesn't. It does have padding, but not a lot.