R value of mattresses in huts - query

In term of R value, I would put them as high as anything. I routinely slept out this winter at Blyth Hut when it got down to -5 or so and I was toasty warm in a lightweight bag, huts provide alot of warmth just in eliminating wind and air movement alone, but in summer they can be hot. Keep in mind ALL sleeping pads have 100% vapour proof fabric, so it theory they are no hotter than anything else, moisture can't pass through a Thermarest either, it's just the type of fabric they are covered with. The problem with a quilt is that you won't necessarily have anything between you and the mat except clothing, so wearing long pants and sleeve will help you sleep better in my experience.

My impression of DOC mattresses (or anything that gets its R through a large bulk of material like they do) is that at the start they are a large drain on your body as the top layers heat up drawing warmth from you, but as the night goes on and the steady temp gradient establishes itself across the 100mm, 10kg of mattress I have the opposite issue: they become too bloody hot - a reservoir of heat - and I start sweating. So yes they do have a high R but initially are a high drain on thermal energy due to their high thermal mass (bulk/volume) compared to a much slimmer sleeping mat of similar overall R.

I generally top vinyl hut mattresses with a light closed-cell pad as they are just too cold for my comfort.

I find them sweaty

Don't know why they bother supplying them - they are uncomfortable (sweaty) and attract mould. Easy enough to carry an appropriate air mattress these days. Would just need a layer of ply-wood on some bunks. Seem to recall years ago some huts had pillows (e.g. Homer Hut). They have long gone and not missed.

I've probably spent as many nights on doc mattresses as in my own bed in my 20 years working nz's backcountry. And gotta say I'd take a DOC mattess over just about any hotel mattress I've met in the same time for comfort. Chuck a sheet over them to avoid sticking to them and they're ok. Never ever swapped a doc mattress for the sleeping-mat on the floor. Whereas hotels & hostels there's probably a 1 in 2 chance of that happening - much to the missus's dispair. Guess it's what you're used to. Or that you can get used to anything!

In the end, I was comfortably warm with the quilt in the huts on the Kepler Track in early February this year. I used a silk/cotton liner to avoid sticking to the mattress. The weather was cool (that massive storm that dumped a metre of rain in a few days) but despite this, in one hut it was so hot in the upstairs dorm that I dragged a mattress into the kitchen to get some sleep.