NeoAir Uberlite in 2021?

^^ Good choice. Get a good warm enough comfy nights sleep. Test out the uberlite when you’ve got borderline conditions on a short trip near home, like Harriman this fall with the leaves in color!

In any case, for me it’s really between the Uberlite, Xlite, or my tried and true Xped Hyperlite medium wide (15 oz).

But you only own one of those right? In that case, it is easy: Take the Xped. The XLite will probably be a bit too cold. I mean sure, you could experiment, but you are going on a long through-hike, right? That hardly seems like the right place to stretch the envelope, and figure out when it makes sense to take one pad or the other (based on the weather forecast). The XLite doesn’t make sense (for you) since the weight savings are so minimal and it is less comfortable (for you). The XTherm doesn’t make sense because the Xped is pretty warm, and again, is likely to be more comfortable. Go with the pad you have.

@YoYo —  A couple notes. You may have meant to write “Perhaps the north Cascades are colder”, but you implied that Rainier is not part of the Cascades. The range is largely defined by the volcanoes (from California to Washington), although it includes some of the mountains a bit beyond, into Canada. This makes the fact that the northernmost volcano (Mount Baker) is not part of the North Cascades National Park a geographic anomaly. In any event, Mount Rainier is definitely part of the Cascades.

The weather around Rainier isn’t much different than the weather on the PCT in Washington. But as you get further north, it may get a bit colder. In late July and early August it tends to be very nice, as you described. But not always. Cold and wet weather is very common as well. The weather source you referenced didn’t mention a location (or I didn’t see it). The report for Marblemount shows an average low of 52 degrees. Marblemount is about 300 feet above see level. So figure at around 3,300 feet it would be 42 degrees (and colder if it is clear). This sounds about right. Figure typical variance of around 5 degrees or so, along with occasionally camping higher (and maybe even lower). So I figure you would have a range of about mid-30s to high-40s as your low, unless you get unusual weather.

The Neoair x-lite R=4.2 is  higher than the R 2.9 of the Exped. I have an Exped UL (72″ x 20″ rectangular) that has the same fabrics and insulation as the hyper lite (the hyperlite is exactly the same as the UL except that it has the mummy shape that shaves off a few ounces). My experience is that the X-lite is noticeably warmer than the Exped. Also, the X-lite uses 30D fabrics, whereas the Exped uses 20D. You would think that the X-lite, having thicker fabric, would be less likely to develop leaks compared to the Exped.

I DO like the baffle orientation of the Expeds better than the horizontal baffle orientation of the Neoairs, but in the end I went with the extra warmth (with no increase in weight) of the X-lite (compared to the medium Synmat UL, 20″ x 72″ I have).

My take is the Xlite is the best balance of weight and durability.