Sleeping Pad Combos - R value question

[Desk Jockey]

Is there a way to determine the r value of combining pads?

For instance, I tend to like to take a thermarest z lite that doubles as a sleeping pad and sitting pad for camp and glassing. For sleep I use thermarest neoair Xlite on the Thermarest.

The z lite has an r value of 2.6. The xlite is 3.2. So what are they combined?

 

[motts]

I remember reading somewhere that they are additive, so your two pads combine for an r-value of 5.8.

I've been wrong before though . . .

 

[Beendare]

Seems to me that 'additive' would be accurate...from experience anyway. My Exped is about 4.5R if I remember correctly, good to about 20 deg with a down bag [about zero with a Syn bag]

Add a waffle matt below that Exped and it would have to be serious minus degree weather to feel the cold I would think.

 

[Jimbob]

The real question is does it matter which ones on top?

Will it be warmer with the the closed cell foam on top and the air pad underneath?


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[USMC22]

The real question is does it matter which ones on top?

Will it be warmer with the the closed cell foam on top and the air pad underneath?


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I’d think the closed cell on the ground just based on experience. A lot of it is coming down to thermal efficiency. An inflated pad is going to be robbed of heat faster than a closed cell foam pad.

 

[Jimbob]

I’d think the closed cell on the ground just based on experience. A lot of it is coming down to thermal efficiency. An inflated pad is going to be robbed of heat faster than a closed cell foam pad.

So wouldn't you want that more "efficient" closed cell right next to you?

 

[Trial153]

From a practical standpoint the closed cell foam would protect the inflated pad from ground damage as well. I think that alone negates any difference in the postion.

 

[USMC22]

I’m not doing a great job of explaining it but the closed cell would make a better barrier to the ground which would rob heat.

 

[Jamo]

I've researched this a bit as well and found that, as others have mentioned, additive seems to be the correct answer for the multiple sleeping pad R-value question.
As to which pad would go on top? According to a few forum posts I've read on backpacking light, they say, "in theory", the closed cell would go on top as it does not transfer you body heat out to the far corners of the pad like an inflatable does.
However, I've always run my closed cell pad on the bottom and inflatable on top in the winter time. I try to run a quilt that covers the edges of the inflatable pad a bit as to not have it exposed to the cold outer air and feel this also helps.
I'm kind of with USMC22 when it comes to running the closed cell on the ground as I feel if the inflatable is against the ground, and the closed cell is between you and the inflatable, then the inflatable inner temp would/will possibly eventually reach ground temperature or simply not warm up much from you body heat?

 

[camelcluch]

I would think that the combined rating is greater than the two ratings added together. Although I think faulting to the two is a good minimum.

 

[renagde]

I've researched this a bit as well and found that, as others have mentioned, additive seems to be the correct answer for the multiple sleeping pad R-value question.
As to which pad would go on top? According to a few forum posts I've read on backpacking light, they say, "in theory", the closed cell would go on top as it does not transfer you body heat out to the far corners of the pad like an inflatable does.
However, I've always run my closed cell pad on the bottom and inflatable on top in the winter time. I try to run a quilt that covers the edges of the inflatable pad a bit as to not have it exposed to the cold outer air and feel this also helps.
I'm kind of with USMC22 when it comes to running the closed cell on the ground as I feel if the inflatable is against the ground, and the closed cell is between you and the inflatable, then the inflatable inner temp would/will possibly eventually reach ground temperature or simply not warm up much from you body heat?

This is what I have found as well. I believe Theremarest ran an article about this on their website awhile ago. Pads are additive so combined you should have an r value of 5.8. And yes, it is true that theoretically closed cell on top of inflatable would be better for r value, but closed cell under inflatable is definitely better for durability. I think you'd have to be sleeping in sub zero temperatures to be able to tell the difference of r value between closed cell on top or bottom.

 

[rayporter]

I have ran a system like this for many years and feel the closed cell on top is warmer, even at 15to 20 degrees.

once with cots the temps were below zero and with a closed cell alone on the cot I was fine.

with a self inflatable I would have froze.

 

[Where's Bruce?]

I always use a EXPED pad with an R rating of 6 with a zero degree EE quilt...every season. It's never uncomfortable. Easy to vent and if the temps plummet (and they will) I'm still good. Used to play the guessing game with different pads and quilts/sleeping bags but not any more.

 

[Lawnboi]

I don’t know about r value, but I run the same system. Zlite, which I use for camp as well and an x lite.

I start feeling the cold with the x lite when temps dip to the 20s. With the zlite underneath of been good to single digits, which is the coldest I’ve had this system in.


Closed cell foam pad also gives me a backup if my inflatable pad fails. Always bring atleast a section of zlite regardless of weather.

 

[duchntr]

Numbers should be cumulative. Put the closed cell on the bottom.

 

[Seaskihunt]

Yep. R value is cumulative.
My 0° EE quilt and Xtherm work quite well from down to right around 0°F up to 60° or so. Much warmer than that and I have to switch to a less insulated pad or I sweat like mad, even venting the quilt.

 

[15layherb]

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