Thermarest describe this incredibly light and compact pad as "the absolute lightest insulated air mattress available," and after some digging around the web we are struggling to argue with that. At 250g for our regular size model it is very impressive indeed and, more importantly in the volume-strapped world of bikepacking it easily rolls down to a size not much larger than a can of coke. That alone was enough to make us sit up and take notice, and it made a big difference when packing up our usual luggage quota.
Of course that very saving in space and weight comes with a compromise on materials and potential longevity - as with all superlight kit you have to take more care, being particularly careful to keep it away from thorns or sharp sticks and stones. We didn't have any punctures through the test but it did feel fragile, adding a more 'crinkly' note to the usual squeaks and groans of using an inflatable mat. We just made sure the included repair kit was always in the bag in case the worst happened - but if it did you would be crying into your morning porridge with that salty £190 price tag.
But despite all this fragility it was extremely comfortable, as you would expect from a 2.5 inch deep inflatable mat, and we found it warm enough for some trips deep into a Scottish autumn. The official R value is 2.3 on the latest version, which Thermarest describe as being on the cusp of a 3 season pad, but we reckon it should be an easy three season here in the UK, depending on how much you feel the chill.
Having used other systems like the Exped Synmat with its one way inflation and dedicated pour-the-air-out deflation valves we have gone right off the classic Thermarest valve. It needs constant attention when inflating to make sure the air doesn't just leak back out before screwed shut and adds a significant resistance to deflation, making everything a bit harder than it needs to be.
Ours came with the classic valve, but the Uberlite is now coming equipped as standard with the new Winglok valve that addresses pretty much every gripe we have with the classic version. Although we haven't tried it yet, it sounds like a massive improvement so make sure yours does. The new version also comes with a clip-on inflation pump bag - again a big improvement on the last version that needed squeezed on over the classic valve and would regularly detach and deflate in the middle of the process.