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Rightfoot
11-10-2015, 16:32
When looking at "R" values for sleeping pads is it safe to assume that a Neo-Air with a 3.2 "R" value and a Ridge Rest with a 2.8 "R" value will give you a total "R" value of 6.0? I can handle the math but was not sure if the values could be added like that.

I leave NOBO on March 2nd and have a new Marmot Lithium 0 degree bag. Will the Neo Air be sufficient or should I plan on utilizing both pads. I anticipate tent vs. shelters to be about an 80/20 mix.

Thanks for your input.

CarlZ993
11-10-2015, 18:29
I'm not sure if the NeoAir Xlite & RidgeRest would add up to an R-value of 6. I'm sure some engineer-type would be able to figure it out. Rather than carrying two pads, why not carry the Neo Air X-therm?

Note: I used the Regular size Xlite pad on my thru-hike. It got down to 15 deg or so & I was warm sleeping on it. I own & use the Neo Air All Season (heavier than the X-therm but not as high an R-value). The All Season is really warm.

Good luck in your decision on pads.

FYI - You might consider carrying Microspikes w/ your early start. All that snow gets packed down along the trail & it turns into ice. I saw some people get hurt in the Smokies & had to be shuttled to the hospital (terminated their thru-hike).

colorado_rob
11-10-2015, 19:10
Yes, R values are simply additive, so total R=6 is correct.

I like the 2-pad thing in case the inflatable fails, you still have your R2.9 ridge rest. The fail-safe ridge rest alone isn't enough, IMHO. You can dump the ridge rest and just carry the inflatable if you want when it warms up a bit, like early-mid april.

Just Bill
11-10-2015, 20:15
Yes, R values are simply additive, so total R=6 is correct.

I like the 2-pad thing in case the inflatable fails, you still have your R2.9 ridge rest. The fail-safe ridge rest alone isn't enough, IMHO. You can dump the ridge rest and just carry the inflatable if you want when it warms up a bit, like early-mid april.

Two yeses are better than one...
Enjoy your hike.

redseal
11-17-2015, 18:48
Make that 3 for yes. Here is a link (with some more links inside) that have some other technical info. http://www.backpackingengineer.com/engineers-guide-sleeping-pad-final-frontier/

Tipi Walter
11-17-2015, 21:58
Yes, R values are simply additive, so total R=6 is correct.



I would like to believe this but I'm not so sure it is true. I used to use an Exped downmat at 8R on my winter trips and, well, it was very warm and comfy. Then it had a blowout and I went with a Thermarest inflatable at 4R with a Ridgerest Solar at 3.5R. Together? 7.5R---and not as warm and never will be as warm as the Exped at 8R.

I think it has something to do with a single high Rvalue pad generating more heat than two separate sandwiched pads with the same Rvalue losing something in the sandwiching.

If I could keep the Exped in my Circle of Trust and use it without thought for dozens of nights I would and it would be my stand alone winter pad. It is amazingly warm (you got geese underneath) and wonderfully comfy. But when it blows a baffle all bets are off and will never be trusted again. Except for sleeping in the back yard during cold nights.

Casey & Gina
11-17-2015, 22:32
I think it has something to do with a single high Rvalue pad generating more heat than two separate sandwiched pads with the same Rvalue losing something in the sandwiching.

I think the materials involved make a difference. The Solar gets something like 0.5R from the aluminum coating, which only will not necessarily deliver that if used under another mat. The ~3.0R of the thick CCF is more tangible and certain, and I would expect more resistant to non-optimal conditions than an inflatable with large pockets of air, say wind blowing underneath when used in a hammock. Down is a very trustworthy insulator assuming it hasn't clumped up and left a cold spot. Point is there is more to the story than R value alone.

Tipi, do you have any thoughts on the Downmat TT? Only R7 but looks like it may effectively make for a very trustworthy winter mat...

colorado_rob
11-17-2015, 22:55
I would like to believe this but I'm not so sure it is true. I used to use an Exped downmat at 8R on my winter trips and, well, it was very warm and comfy. Then it had a blowout and I went with a Thermarest inflatable at 4R with a Ridgerest Solar at 3.5R. Together? 7.5R---and not as warm and never will be as warm as the Exped at 8R.

I think it has something to do with a single high Rvalue pad generating more heat than two separate sandwiched pads with the same Rvalue losing something in the sandwiching.
Pads "generating heat" ? Wow. Sorry, it's simple physics. Actually, the surface of a pad blocks some heat (teeny-tiny amounts), so two perfectly R=3 pads would have a slightly higher R value than 6. Not less. Physically impossible. One of those silly laws of thermodynamics. But don't listen to THIS rocket scientist. Keep your imagination going!

This all being said, I doubt if a manufacturers' R value claim is perfect, probably scatter all over the place.

Casey & Gina
11-17-2015, 23:31
This all being said, I doubt if a manufacturers' R value claim is perfect, probably scatter all over the place.

Well that is a galid point. There is no standard used by mat manufacturers - they all have their own. Cascade Designs pulls tricks like advertising the warmer R-value of the torso section of their women's mats (e.g. the Prolite Plus) as though it is the value of the entire pad, though it is not. Nemo doesn't advertise R values for this reason, though they do advertise a minimum temperature rating which is equally subjective.

Tipi Walter
11-18-2015, 00:45
Pads "generating heat" ? Wow. Sorry, it's simple physics. Actually, the surface of a pad blocks some heat (teeny-tiny amounts), so two perfectly R=3 pads would have a slightly higher R value than 6. Not less. Physically impossible. One of those silly laws of thermodynamics. But don't listen to THIS rocket scientist. Keep your imagination going!

This all being said, I doubt if a manufacturers' R value claim is perfect, probably scatter all over the place.

I just related my experience and comparison from field use on cold winter nights. The Exped downmat at 8R is noticeably warmer than the sandwiched pads at 7.5R. But heck it must be all in my imagination. Spreadsheets and physics have nothing to do in my opinion with reality on the ground. For non-believers I can ask they try the Exped downmat overnight at 0F and then try the two-pad inflatable/ccf on another 0F night and do the comparison.

And whenever someone says his down bag is warm or his down bag generates heat, there are always those jolly folk who raise the red flag and proclaim down items DO NOT PRODUCE THEIR OWN HEAT!! True enough on paper or to a student of physics, meaningless to real-world backpackers who luxuriate in "warm" goose down and marvel at the amount of our body heat these items conserve and throw back at us---earning the phrase "This down bag (or jacket or pad) is warm!"

A scientist might say my experience is invalid and use neato graphs but what good is a scientist when I'm stuck in a polar vortex at -10F for three days inside a tent? No one knows the working benefits of a high Rvalue pad system better than the guy who sleeps on frozen ground at subzero temps. You either sleep cold or you don't. One part of the equation is the down bag you're wrapped inside. The other is what is underneath. Trail and error is the only way to find what works, not computing Rvalue numbers off a graph, and not adding up Rvalues from sandwiched pads and thinking those numbers will work or are relevant---until tested in the field.

Tipi Walter
11-18-2015, 01:02
Tipi, do you have any thoughts on the Downmat TT? Only R7 but looks like it may effectively make for a very trustworthy winter mat...

Exped has changed a lot of their pad configurations and so the TT model is new to me. They say it is more robust than the older downmats and have a different baffle weld system? Maybe so. But $300 for sleeping pad? No thanks. And when or if a baffle weld seam blows, well, you're left in the middle of nowhere on top of a bulging bladder. It happened to me on the first night of a 19 day winter trip on a newish $200 downmat pump 9 and ever since I can't bring myself to go back to Exped.

I'm not the only one who has experienced such blowouts---

http://tipiwalter.smugmug.com/Backpacking2013-1/19-Days-of-Solitude/i-XgfnnwC/0/M/TRIP%20151%20040-M.jpg
Here's my pad during the blowout event.


http://i0.wp.com/farm9.staticflickr.com/8438/7763776520_3ec41ca4f6.jpg?resize=500%2C375
Not my picture.


http://cache.backpackinglight.com/backpackinglight/user_uploads/1443140599_132476.jpg
Yet another.

Point is, when you're afraid to lay down on your sleeping pad. well, your trip has turned to crap.

Casey & Gina
11-18-2015, 01:11
Trial and error is the only way to find what works

This indeed!

Casey & Gina
11-18-2015, 01:17
I have seen those Exped baffle failures in person and likewise don't feel trusting. The TT is new, expensive, and doesn't have a lot of reviews yet. I suppose time will tell...

Just Bill
11-18-2015, 01:19
Tipi...
.5 R is about .44 CLO which is about 2.2 degrees F.

Now that bit of science out of the way; I was explaining how my quilts are put together to a sewing contractor and how flipping it inside out altered the temps by about 2-3 degrees in the user's favor.
I was given a shocked, skeptical look and told that nobody would notice the difference. I choose not to debate it much. Though both science and real life agree in this case.

At say 30*, nobody is going to notice if a zero degree pad is two degrees warmer or cooler.
At zero degrees, and the temp falls to -2... suddenly that subtle difference is quite noticeable.
But if somebody always has 10 degrees to spare and never pushes their gear the point is lost...

Stacked pads, stacked quilts, and piling on clothes... all things that work better on paper than in real life.
Though we're talking +/-7 degrees of error typically... however that's not the moral of the story.

I like math and science- they let me do some good stuff.
I'd still take 100 nights in the field over 100 days in the lab.
Though 10 days in the lab can save 100 nights of guesswork. ;)

Snowleopard
11-18-2015, 12:35
If the R ratings are both correct, the combined R value will be [almost] the sum of the two. The theory assumes that the layers extend infinitely far in both directions (that would make for a heavy pad). There are other factors that change it a bit, there can be a boundary air layer on each side of each pad that can increase the combined R value a little or there can be air movements that decrease the effective R value.

BUT, the ratings might not be accurate, or have deteriorated with age and use (insulation gets compressed). Backpackinglight.com did tests on insulated air mattresses some time ago, measuring the R value. They found is that the R value is bigger when the pad is inflated more.

If you're feeling cold you can put clothes or packs under you to decrease heat loss to ground. Down or other compressible insulation won't do much here, wool pants work well for this. Once I shared a tent on Mt. Rainier with a fellow who had a super expensive, super warm down sleeping bag. After a few nights, he mentioned that he was freezing. I was too warm with my cheapo EMS 20F bag. It turned out he had no pad at all. The insulation from the snow was the 1/16" thickness of the compressed down. We showed him how to put this clothes underneath and then he was toasty.

rocketsocks
11-18-2015, 13:53
I just look at it like this...cause I don't know the formula for R value.

a warm pad plus another warm pad...equals a warmer pad.

Just Bill
11-18-2015, 14:50
I just look at it like this...cause I don't know the formula for R value.

a warm pad plus another warm pad...equals a warmer pad.

Rocketsocks law of insulative addition.
The best math is no math, lol.

I'm a fan of Tipi's Circle of Trust too-
Fool me once, shame on you...
But I'll be damned if you get another shot.

Despite knowing a bit o' math I always defer to Ol' Man Willy's adage:
"If it don't work in the backyard, it don't work on the trail.
And if'n you ain't been to the backyard, best to go back in the house."