Stacking air mats

[Moondog55]

I just took delivery of another Thermarest mat. Second hand naturally
I simply got tired of the Mountain Designs ones dieing on me and decided to buy a real one.
It's bulky and heavy as are all of the old style camp mats but it is more compact than the RidgeRest I normally use on snow
So I'm wondering if anybody here has stacked an old style CampRest, now called BaseCamp model; under one of the new S2S comfort plus mats to comment on the warmth and comfort and how you went about tieing them together
Using the two together would give a system 4.5 inches thick and with a massive R-Value except that Cascade Designs give the R-value as "5" and converting US to SI units means that it seems that the TR mats is only rated at 0.88R SI which is less than my cheap blue CCF pad so what is going on?
Does Cascade Designs use SI units for R-value?

[Franco]

The BaseCamp has an R value of R5 using the same rating that would give your foam mat R1/1.5 ( R2.2 for the Ridgrest)
I believe the CampRest had the same value.

[Moondog55]

According to the Cascade Designs site but if they are using US R-values that isn't much at all
S2S give an R-Value of 2.6 for their foam filled self inflator of the same thickness

[Franco]

Do they have the same foam and structure ?
(holes in the foam)

[Moondog55]

So many iterations over the decades that making direct comparisons between brands and even different models in the same brand is now impossible I think
I'll just assume that the T'Rest is as warm or a tad warmer than the RidgeRest and go with the comfort factor perhaps.
Yes the S2S mats have tube like holes in them so not as warm as one with more solid foam I'd say.

[Franco]

Not so sure why you want to complicate something really simple.
Thermarest rates their Ridge Rest Classic at R 2.6 and the Base Camp at R5, so twice as insulated.
Why would they use different measurements/scales/standards for the two ?

[Moondog55]

Because Cascade Designs don't tell you which system of measurements they are using.
It really isn't all that simple when you realise I'm planning for an Arctic winter and -40C temperatures.
So actually I think I'm making it simpler by thinking about taking only 2 mattresses rather than a multi combination of 3 or 4 to get the thermal resistance and padding I know I need for comfort
You can't make direct comparisons between different makers products if each manufacturer uses a different system of measurement so while the Camprest may be twice as warm as the RidgeRest I need to know if it will be warm enough to suit my old bones. My mate in the US uses a T'Rest a full 4 inches thick plus CCF pads and reflective bubble wrap at these temperatures and we seem to have similar metabolisms
If Cascade Designs use SI then I'll know that the combination is R-10.6 which should be OK but if they are using BTU or the American equivalent then the total R-Value is a lot lower. A bit warmer than the thickest Exped DM9 mattress at R-8 and I'd be happy I think
I'm overthinking it but not by a lot because I need to get a good nights sleep or I can't function for more than a few weeks.
Here directly on snow I need a multi combination now at -12C
The problem I find with the S2S mat is that it is warmer by a long way when blown up hard but it is more comfortable when a lot softer, I found the same with ThermaRest mats over the years too

[Moondog55]

S2S just got back to me
They take their R0Values with the mats inflated to 0.05Bar/ 0.725psi
I'm told by the feller at S2S that this is about as firm as a mat can be inflated by mouth and that they are indeed less warm at lower pressures
Cascade Designs customer service is very slow, I asked T'Rest 5 weeks ago how they measure their mats and so far I've not had an answer

[Franco]

Because Cascade Designs don't tell you which system of measurements they are using

Let me try again...
Cascade Design tests their mats in house. The same team that test one mat tests the others using exactly the same equipment.
So once you know how insulated their R2.8 mat is (the Ridge rest, I believe you are familiar with ) , you will also know that THEIR R 5 mat is almost twice as insulated.
This is where they test their own mats :

coldlab.jpg (46.59 KiB) Viewed 19500 times

https://thermarestblog.com/r-value-meaning/

[Moondog55]

That may be so but it is irrelevant to my query to Cascade Designs, which was to simply ask them if they used SI units or BTU
It is not possible to tell simply from looking at their website because of the way they mix units in the descriptions. I'm happy to assume they use SI units and that CCs R-Values are SI and the same as other makers from Europe and China
S2S on the other hand were quick to answer my questions and give detailed information about the standard test procedure they use
I don't think you have read any of this post correctly Franco as you seemed to have missed my point entirely; my query was about the units used
There used to be a convention that said if "R" was capitalised it was SI and if it was a small "r" it was BTU but that seems to have fallen by the wayside years ago

[Orion]

That may be so but it is irrelevant to my query to Cascade Designs, which was to simply ask them if they used SI units or BTU
It is not possible to tell simply from looking at their website because of the way they mix units in the descriptions. I'm happy to assume they use SI units and that CCs R-Values are SI and the same as other makers from Europe and China
S2S on the other hand were quick to answer my questions and give detailed information about the standard test procedure they use
I don't think you have read any of this post correctly Franco as you seemed to have missed my point entirely; my query was about the units used
There used to be a convention that said if "R" was capitalised it was SI and if it was a small "r" it was BTU but that seems to have fallen by the wayside years ago

While really odd unit combinations are possible, the difference between typical usage of imperial and SI units for R-value is a factor of about 6. If Cascade Designs and Sea to Summit were using units that differed this much it would be readily apparent by comparing similar products.

On the S2S website, they say an R-Value of 3-4 is appropriate for "Early Spring/Late Fall" and R-Value 5+ for "Winter". On the Cascade Designs website they say "...you can generally draw the line between three-season and winter mattresses at an approximate R-value of 3.0".

Sounds like the same thing.


I'm surprised that the S2S engineer believes you can only blow a mattress up to 0.05 bar. I've measured my own ability blow into a tube and was able to get to better than twice that, just with my lungs. If I used the muscles in my cheeks I could get to about three times that value. That's typical for a healthy adult. I usually blow my mattress up to the maximum of my ability to inflate. It wouldn't be easy to measure the pressure but I've always assumed it was something around 0.10 bar. Of course to maintain maximum you have to inflate it a second time because the air cools. And if, like me, you own mattresses that slowly leak you have to inflate it again at 3am and sometimes yet again at about 6am.

One thing I would wonder about stacking inflatable mattresses is stability. Many of them are slippery as eels and stacked they could be quite frustrating. If this is a problem one possible solution is to sandwich them between thin ensolite pads. I routinely carry a 3mm ensolite pad that I put under my Thermarest. It keeps it from slipping around and also helps protect the eggshell like fragile exterior material.

[Franco]

from the 2011 Backpackinglight survey (by Roger Caffin) :
What is this R-value that you read about everywhere at Backpacking Light? It is a measure of thermal conductivity – or how fast your body heat drains away to the cold ground underneath. Technically it is the ratio of the temperature difference across an insulator to the flow of heat through the insulator, and there is a strict analogy to an electrical resistor (R=V/I). However, while SI or metric units are given as m2·C/W, it can also be expressed in imperial units of ft2·F·h/Btu. The numbers for imperial R-values are about six times those for metric R-values and they are only used for building insulation products in America. We will not mention imperial R-values again.

https://backpackinglight.com/airmat_sotmr_part1_2011/

I still have no idea how Moondog would come to the conclusion that the Basecamp, a mat that is meant to be for 4 seasons and has all reviewers confirming that , could possibly be R 0.88 and that was the reason for my comments above.

[Mark F]

I think you will find that most mat manufacturers quote R values in imperial units. Multiply the 0.88 by 6 to get a reasonable imperial R value for a 4 season mat of 5.3.

Most manufacturers use the imperial R values because they deliver bigger numbers - would you buy a mat rated R0.88 or one rated R5.3?

A bit like all the real estate ads for mini farms quote the area in acres not hectares to make it seem larger.

Edit - just checked WIkipedia and the conversion value is 5.68 so 0.88 x 5.68 = 5 https://en.wikipedia.org/wiki/R-value_(insulation)

[Franco]

I think you will find that most mat manufacturers quote R values in imperial units. Multiply the 0.88 by 6 to get a reasonable imperial R value for a 4 season mat of 5.3.

Most manufacturers use the imperial R values because they deliver bigger numbers - would you buy a mat rated R0.88 or one rated R5.3?

A bit like all the real estate ads for mini farms quote the area in acres not hectares to make it seem larger.

Edit - just checked WIkipedia and the conversion value is 5.68 so 0.88 x 5.68 = 5 https://en.wikipedia.org/wiki/R-value_(insulation)

No, they don't. They all use SI metric values.
Read again the comment I posted from Roger Caffin's article.

Maybe to explain a bit better my point about measurements , this is the S2S Comfort Plus

S2S Comfort Plus.jpg (10.78 KiB) Viewed 19356 times

785 g, 8cm high (top of bubbles) rated in SI as "equivalent to R5.
this is the TR Basecamp

BaseCamp_angle.jpg (14.67 KiB) Viewed 19356 times

it's full foam, no bumps no empty spots inside.
5cm high, 970 g , rated at R5,
Now doers it make sense to think that the Basecamp is in fact 0.8 in SI ?
Who would buy it if it was ?

[Mark F]

Roger got it wrong! Unusual but true. Read the Wikipedia link.

Edit - have a look at ultralight outdoor gear where they do quote the R values in SI units. https://www.ultralightoutdoorgear.co.uk/equipment-c3/sleeping-mats-c58/ultralight-airbeds-c138/neoair-xlite-small-sleeping-mat-p3614 The link takes you to Neoair Xlite and cites an R value of 0.56. Cascade Designs gives an R value of 3.2. (0.56 x 5.68 = 3.18) Check the Specification tab on the link where both R values are shown.

[Franco]

BTW, I'm reading another Arctic expedition book.
last night I came across a comment about a bunch of guys that were wondering on ice, lost, starving for the most part.
In there it stated that when starving no amount of blankets could keep them warm at night, however on the few occasions when they had a full belly , they slept warm.(you can only be warm if you have calories to burn...)
This is partly the reason why at times we get totally conflicting comments about the same mat .
(apart from that, my wife, as an example, always sleeps much colder than me, so another reason)

[Moondog55]

Well having spent a night on the T'Rex mat subjectively it isn't as warm as the S2S one or as comfortable.
Cascade Designs still have not replied to my email and despite reading through their website again I see no information regarding the units of measurement used.
I'd really like to think that the R-Value given in in Metric but I'll only be mildly surprised if it goes the other way
In many ways it was and is a whinge post about the poor customer service/communication issue.

[Orion]

Cascade Designs still have not replied to my email and despite reading through their website again I see no information regarding the units of measurement used.
I'd really like to think that the R-Value given in in Metric but I'll only be mildly surprised if it goes the other way
In many ways it was and is a whinge post about the poor customer service/communication issue.

It's hard to get technical responses from companies. From what I've heard Cascade Designs is pretty good about dealing with product problems. I'm going to be testing this out shortly as my ~1 year old Xlite pad blew a baffle and I think this should be covered under their warranty as I was using it exactly as described on their website. We'll see.


With regard to the R-Value, while it's annoying that the the units are routinely omitted you can take a different approach. Do an estimated calculation yourself.

Looking up the thermal conductivity of ensolite on the internet I find a value of 0.040 W/(m-K) specified on one manufacturer's website. The R-Value is the reciprocal of the thermal conductance, which is the thermal conductivity through a unit thickness of material. In short,

R = d/k, where R is the R-Value, d is the thickness, and k is the conductivity.

So for a 1.5cm thick pad (like the MEC Zotefam Winter pad), you would expect the R-Value to be approximately:

R = 0.015m / 0.040 W/(m-K) = 0.375 m2-K/W

But MEC says their pad has an R-Value of 2.1. That can be explained by assuming they are using imperial units: 0.375 m2-K/W = 2.1 ft2-°F-hr/Btu.

Similarly, the Cascade Designs RidgeRest, which is also 1.5cm thick, has a stated R-Value of 2.6. This is in line with imperial units. The fact that the R-Value is higher could be due to the ridges or possibly due to a different testing protocol. Either way, the R-Value is clearly NOT in SI units.


Frankly, I find R-Values are about as useful as sleeping bag ratings. They are just something to keep you from really screwing up. When it comes down to what you actually need, specific conditions and also one's own metabolism have such a large effect that these ratings are far from being definitive guidelines. My wife routinely sleeps on a 3/4 length pad with an R-Value of 3 on the snow in the winter. She's a warm sleeper.

[Moondog55]

Yes perhaps true but I am much more likely to buy from a company that does respond to technical inquiries.

[Franco]

Orion,
you could be right that the industry is using Imperial rather than SI, although that would make the response from S2S to Moondog incorrect and he seems happy with that...( is the wrong answer better than no answer ?)
Anyway, looking around the net I see that if a specific comment about the units used is made it seems to be always about SI but if those R values are compared with the wall insulation numbers given in the US (in Imperial ) they appear to be closer to those.
My point really was that it looks to me that S2S , Thermarest , Exped and the rest all use the same units.
Now because the type of insulation , structure and perforation differs from mat to mat , that needs to be taken into consideration but when a somewhat similar perforated foam is used they appear to be pretty comparable.

[Orion]

Franco, I completely agree. But since Moondog was interested in the units I thought a simple calculation would likely make it clear. And I think it does. Plus it's in line with what Mark F. posted and I know Mark is a really smart guy. Roger is a smart guy too but nobody is infallible. Or maybe I'm wrong, but I don't think so. It's weird that imperial units seem to be the unwritten standard for this. Maybe it's like Mark suggests, the imperial units result in bigger looking numbers and the marketing guys love that.

I must have missed where Moondog said that S2S told him they used SI units. Did they?


A related question: How do you go about figuring out the R-Value you need for a particular set of conditions?

[Franco]

Franco, I completely agree. But since Moondog was interested in the units I thought a simple calculation would likely make it clear. And I think it does. Plus it's in line with what Mark F. posted and I know Mark is a really smart guy. Roger is a smart guy too but nobody is infallible. Or maybe I'm wrong, but I don't think so. It's weird that imperial units seem to be the unwritten standard for this. Maybe it's like Mark suggests, the imperial units result in bigger looking numbers and the marketing guys love that.

I must have missed where Moondog said that S2S told him they used SI units. Did they?


A related question: How do you go about figuring out the R-Value you need for a particular set of conditions?

He did not but was implied when he stated :

(The BaseCamp has an R value of R5)
According to the Cascade Designs site but if they are using US R-values that isn't much at all
S2S give an R-Value of 2.6 for their foam filled self inflator of the same thickness

( I later pointed ot that the Basecamp is solid flat foam, the S2S is perforated and the bumps are at the same height not the valleys)

[Moondog55]

Copy of my email from S2S

Hi Ted



As an Australian company, all our measurements and specs are in metric(unless stated otherwise). Our R-Value of 5 is equivelant to an imperial R-Value of 28-29, more than suitable for your requirement. The Comfort Plus Insulated model is about 63mm thick. While this isn't the 100mm you've been recommended, the warmth rating is much higher than recommended. This is achieved by using Exkin Platinum coating on the interior of the outer fabric, this reflects radiant heat from the user back up to them, and radiant cold back to the earth away from the user, similar to an emergency blanket. The mat also has Thermolite insulation throughout the interior of the mat, which prevents convective heat transfer through the mat.

[Orion]

Thanks for that, Moondog.

So I guess I'm wrong about everybody using imperial units. It's mighty confusing as S2S doesn't say (on their website) what units they use either. And kind of odd that the R-Values of their pads are in line with the R-Values of similar pads made by Cascade Designs.


What kind of pad did Scott use?

[Moondog55]

I believe Scott and that rest of the party relied on the integral value of the caribou skin sleeping bags with canvas ground mats and the spare clothing underneath.
A few of the fellers I exchange emails with in Canada and Alaska use caribou skins as their ground mats too

[rcaffin]

Hi all

Could I have got it wrong? Of course. My measurements were ratiometric, not absolute. I had some different layers of foam calibrated for me by someone else in America, and I was told these were SI units. But if that person got it wrong, then we have all been mislead. It would seem quite possible.

Now, the comment from S2S is all very well, but I suspect they are ASSUMING that their R5 value is SI and are then only calculating what the American R-value would be. I question whether they had actual measurements done. The rest of their spiel, about platinum coating .... have you seen the cost of platimum? Forgive my doubts.

Exped get their mats tested in an independent Swiss lab (producing 'reasonable' values), but I note that the web site is also quoting temperatures in degrees Fahrenheit. I suspect they have converted their SI results to imperial for the American market.

Cheers
Roger
PS: Scott - I am not sure they had any mats. You will note, if you read Scott's description, that the ice under them always had a shape hollowed out to match their bodies in the morning. Also, I don't think they ever slept 'warm' while sledging. Brutal stuff.