Complimenting sleep system

The R-value of a mat is how much body heat it retains between you and the ground. A higher R-value will keep you warmer in lower temperatures, so it's gonna be a better use of weight than your sleeping bag in my experience. Obviously, you need a warm bag, but for example, I can get by with a 20º bag to about zero if I'm using my X-Therm mat (high R-Value) and I can't do that with my Z-Lite (low R-Value).

So, A little more R-value goes a lot farther than sleeping bag degrees.

I'm still not clear on how the R value compliments the temp rating on bags. Specifically, how is the performance of the Versalite different with the Dowmat vs. the Synmat?

The sleeping bag provides insulation above and to the sides, but not beneath you. That's the role of the pad. For example, take a zero degree bag snow camping; if you only have the 3.1 R-value mat under you, you will probably feel cold coming from the ground.

I'd like to make sure that the combo of a 32 degree bag and 3.1 R-value mat keep me warm with just a baselayer in the 40s.

For myself that would be sufficient; for a cold sleeper you might want to add a thin CCF pad to the Synmat.

And I'm curious how I could develop alternate pairings like the Summerlite with the Dowmat or the Versalite with the Synmat to optimize weight for the temp.

Refer to: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=20434&skip_to_post=163242#163242

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Thanks for that article link, Jeremy – very helpful.

I'm also curious as to which other bag companies would be zipper compatible with WM bags. Does anybody have insight on this?

Dan,

If the cute hiker from my trip needs to share a tent this weekend, I'll let you know. For science!

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Yes Jeremy, thanks for the link. I've been down a deep rabbit hole since I clicked on it 2 days ago. :-/

From that link, I uncovered these relevant links:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=60666

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=16189&startat=60

The basic equation is (R value of Pad * .18 for side sleepers or .35 for back sleepers) + (R value of Bag * .82 for side sleepers or .65 for back sleepers).

I get that. What I'm missing are the R values for WM bags and then a table for converting the combined R value to a temp rating. I believe the temp rating is available on the sleeping bag primer on page 30 of http://www.mammut.ch/images/Mammut_Sleep_well_pt1_E.pdf, but I can't get a good read of the chart because the pixel density is too low (the image blurs as I zoom in).

I do have the EN13537 standards test results for the WM bags, can I back into the R-value using the EN13537 degree ratings?

Hi Sean,

I'd point you to Richard Nisley as this goes outside my knowledge. I also have some uncertainty regarding the units. Specifically, I don't know if the sleeping pad values mentioned are in US units or SI units. Per wikipedia, the US unit value = 5.68 times the SI units. There are probably other factors at play as well.

In your PDF, please refer to page 32 as well. "K·m²/W" is the SI unit, the value of which I suspect* you may be able to derive for your bag as follows:

R-value = (31.81 – $EN_COMFORT_RATING) / 36.36
(Use degrees Celcius)

* Taken from: http://www.trailspace.com/forums/gear-selection/topics/91375.html

I ponder sleep systems and have an interesting setup this weekend.

I have a 20 degree 850 fill down bag and a 40 degree 600 fill down bag. I have an Exped Synmat 7 (with pump – not UL version). I've been comfortable in the 40 degree bag in the low 50s with a light base layer. Comfortable in the 20 degree bag down to 21 with a mid base layer, 100 weight fleece and hat.

This weekend is supposed to be 38 on our trip. The question is do I take the lighter, smaller 40 degree bag and stretch it with extra clothes – or the 20 degree bag and be cozy with less clothing. I tend to carry dedicated sleep clothes so taking stuff to sleep in with the 40 degree bag may offset the benefit of the smaller bag…

I'm still dialing in what works in what temps – but will say that I really love the Synmat 7 – makes me want to look at the UL version as the only thing I don't like is it's a bit heavy – but the 21 degree night was the best nights sleep I've had since I started camping a few years ago… I'll take the weight, however, as I sleep so much better on it as a side sleeper who tosses around a bit…

…..a sleep system:
" nice sleep system, very nice!" ;)

On a side note, if you assume the R-value of 3.1 for the SynMat UL 7 is in the US units and work backwards:
31.81-((3.1/5.68)*36.36) = 11.97 (equivalent EN comfort value in degrees C)

It suggests that the R-3.1 pad is "comfortable" down to about 54 F. If you sleep warmer, or find the "lower limit" ratings are a more accurate measure, you could easily go lower. (Many have.)

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Thanks, Jeremy. I lit up the bat signal for Richard. Let's see if he'll chime in!