So, I've now been using car sunshades, aka AutoShades for fall and winter camping for a couple years.
For reference I'm referring specifically to this:http://www.bikepacking.net/reviews/sleeping-pads/car-sunshade-sleeping-pad/
They are absolutely superb for *supplement* insulation. I highly recommended them for their durability / indestructibility, light weight, ease of use and generally great r-value. What's more after a drought in which I could not find replacements I have realized they're now stocked at Meijer for about $7 or $8. What's more though auto shade designs will change I suspect they will be around for a long time to come. Not that I'm taking any chances, I'm stockpiling them.
A typical favorite use example is that it is always the first thing out of my pack. Which is great because it needs no protection from the elements. It doesn't even hold water. Indeed I use it under my super twinkie seat bag sometimes to keep the mud off my *rse. You can even just wash it in a stream and be sleeping on it five minutes later.
But anyway, back to the point... used scenarios.
It's perfect for throwing down in the snow or on a wet bench or in the dirt to sit on to keep your butt warm and dry.
Indeed it's accordion fold design lends itself to a perfect sized sit mat every time.
They are especially great around the fire since they are very resilient to flame and even if you do burn some spark holes in them... hey.. they're only $5. You can afford to buy yourself a new one each trip.. not that you'll need too.
In this respect they are the perfect compliment to an insulated air mat or DAM (down air mat) which are to delicate and take to long to deflate / inflate to be used and / abused in such a way... especially around a fire.
Another great use example is simply adding it underneath your bivy / insulated airmat / sleep system not just another thermal layer but also another layer of protection from abrasion and potential puncture.
You simply can't go wrong with them as a supplemental in the winter or even as a minimalist UL solo pad in the summer and early fall, but herein is the issue:
I'm seriously thinking of using TWO on the divide in mid/late October as my only sleeping mat and I will most likely encounter some snow.
Furthermore while I have one extensively as supplemental insulation for years I have never in all my use tried to use them in the snow by themselves as my sole sleeping mat.
AND... I have no way of testing them in the snow before I go.So, the questions are:
1) does anyone have any experience with them in the snow as a solo sleep mat?
Again, I think two should have some serious r-value, but have no way of knowing.
2) does anyone know of any way to run my own r-value tests?
I have at least a basis for comparison since I own several mats including a Big Agnes primaloft insulated Aircore, a Thermarest Z-rest, and an Exped Airmat.
I do have fairly extensive winter experience with these sleeping mats here in Michigan. By "fairly extensive" I mean, the newest one and one I've used the least, the Big Agness Primaloft Insulated Aircore I used for 25+ nights on my 30+ day January trip down the eastern divide last winter both in snow and in temps well below zero.
Indeed it is the three time failure of this Big Agness Aircore mat that was the biggest issue on that trip. Pretty much the only issue in an otherwise great trip. It failed near the valve stem, probably due my sliding in and out over the valve stem when entering my bivy. The worst part was not the three restless and cold nights, but that it destroyed my confidence in being able to camp at altitude causing me to have to completely change my hard charging, late riding, always remote camping, trip dynamic. Specifically I couldn't ride late into the evening, night ride over passes, ended up staying in a lot more hotels and retreated from at least one storm on the BRP (Blue Ridge Parkway) to the valley because I couldn't be sure of getting a good nights sleep.
I finally succeeded in sealing the holes (multiple pin holes at the corners of the valve seam) well and restoring my faith in it with some Shoe Goo, but by then the trip was pretty much over and the damage done.
Unfortunately I'd opted not to take an car sunshade on that trip.
I really wish I had.
I do love the Aircore, its thermal properties are superb and quality high but it is absolutely not for bivying and I really wish I could take my Exped Airmat's huge and indestructible valves that make it so easy to blow up and put them on the aircore. Indeed... I'll probably at some point get an Exped 7 XS weighing in at 21.9 oz.
But back on point. It is because of that trip I've decided that while I love air mats because when they work they work extremely well... that they're to high maintenance (inflating / deflating / patching) and too delicate for longer trips, i.e. more then s24o, 48, 72 or at max week long trips. Not that I won't use them in the future for specific conditions (I love my Exped and in 2-3 three years heavy use its never failed me) but I don't want to rely on them for longer trips again.
Thus we come back to the autoshade.
Extremely light. (5oz before trimming down)
Relatively compact packing.
Great as a supplemental.
Like so many of my favorite pieces of UL bikepacking gear (i.e. alcohol stoves) they seem to cheat the rules of expensive specialty gear and high dollar materials.
...but what is its R-value???