Exped Synmat UL 7 felt “cool” under hips at 5-8 deg C

My first reaction is that I would never sleep in boxer shorts and t-shirt. One of the cardinal rules of cold weather camping is to wear at least some of your insulated clothing/base layers to sleep. It not only helps supplement your comfort but also keeps your sleeping bag much cleaner.

I think the idea of putting a small section of thin foam (perhaps dual use as a sit pad or frame sheet) under your hips is an excellent idea in colder conditions.

is a little lower than some alternatives. It's a smidge over R-3, which compares to a tad over R-4 for some other popular air pads like the Big Agnes Insulated Air Core. That means the Synmat allows about a third more heat transfer at any given temperature difference, other things being equal. I'm not criticizing the Synmat–I love mine–just pointing out the specs.

There are many ways to lose heat at night, and conduction to the ground is only one of them. You mention that your Synmat UL7 was fully inflated – that's good, as the insulation value is a factor of how full the pad is. Is your sleeping bag accurately rated, and is it new / clean? How well does your tent block wind? Did you eat well before you went to bed, and were you well hydrated? What's your metabolism like? Was your site in a valley, near water, or in another location that could have caused the localised temperature to be lower than in surrounding areas?

First time I took my Synmat UL7 out, I made a lot of mistakes. It was early season, my sleeping bag wasn't rated high enough, I was probably dehydrated, and I pitched camp in a valley close to water. Each time since I've made adjustments, and the mat has been comfortable down to ~3-4C. When it's borderline I will add a 1/8" closed cell pad to add an extra layer of insulation. But when I expect temps below -5C I'll switch to my Downmat UL7.

Just don't expect the mat to be a panacea – you have to be mindful of other factors.

Thanks for the comments so far. Stuart D – yes to all the above. I was car camping, so I was well-fed, well-watered, well everything and using my warm double-walled tent with fabric inner and my sleeping bag rated to -5 deg C. It's not new but it is clean and the reason I sleep in boxers and a t-shirt in it is otherwise I overheat! I had to keep the side zip and the toe-box zip open most of the night. So, my body wasn't cold. But even while feeling otherwise toasty warm, when I lay on my side I could feel "coolness" under my hip, which I'm concluding was either localized heat loss at that point, or my imagination.

Stuart D, when you say "the mat has been comfortable down to ~3-4C", do you mean -3 to -4 deg C, or +3 to +4 deg C?

On a hiking trip (as opposed to this car camping trip) I would be in a "colder" tent, wearing all my layers, and using a quilt. So, if I wasn't imagining things and the Synmat is borderline at the temps I normally encounter (0 to 5 deg C), should I swap it with the Downmat (add 105g), or use a bit of foam under the hips (add ?g)?

BTW, the minimum air temp was likely in the range 5 to 8 deg C with no significant wind chill. The car next to me registered 5 deg C, mine registered 8 deg C, and a thermometer at a nearby house registered 8 deg C.

UL 7 plus 1/8" foam mat (GG?) down to -7 C. We were warm.

The secret is to NOT camp on a hard smooth surface. If you camp on a lumpy surface (oh the horror!) you can always find somewhere between the lumps for your hips. Then the mat is not so thin.

Cheers

Thanks Roger. Any idea where one can buy a 1/8" foam mat in Australia?

I was also thinking of a quilt but i have never uswed one yet to see the difference from sleeping bags. My current sleeping bag is Monbel UL super spiral down hugger #3. I think it might feel strange to sleep with my head and arms outside the quilt.

@Matt – I meant approximately +3C to + 4C. I tend to think in Fahrenheit after the best part of two decades living in the US, so conversions back to Celsius / Centigrade are a little rough and ready.

I typically take a torso length 1/8" closed cell pad with me regardless of temps, as a little insurance against cold and sharp objects. I ruined my first Synmat UL7 with a large scratch from a dog's claw. He didn't slice the pad wide open, but the pad never held air for more than a few minutes after that.

Roger's advice is good, as always.

+1 to Roger’s recommendation. On the last few trips I have been a little cool on my Big Angus Insulated Core. I was just chalking it up to me being a cold sleeper in my quilt. On my last trip to Scotland some cold temps were projected, so I also brought a torso length InsuLite 1/8" Foam Pad.

As it turns out, I’m not quite the cold sleeper that I thought I was. I made it through -14 deg C night with my quilt and some extra clothing. My son, who is a warm sleeper, over heated almost every night in his golite 20 quilt. Before this trip, I would not have thought an extra 1/8’th of an inch would have that much of an effect, but it certainly did for my son and I.

My synmat UL7 has felt cool under my hips and shoulders at about that temp (0-4 C). On one trip, I remedied that problem by piling a layer of pine duff under the pad to separate it from the cold granite. A thin CCF pad would have worked, too.

+1 to Colin

+1 Roger and Colin

I've owned and used both the UL 7 and original 7 with snow camping and some winter non-snow camping. These pads will conduct too much heat from the air-cells into the ground unless paired with thin ccf pads. Torso length works OK and full length is even warmer. My guess is that there is enough air circulation inside the UL 7 that the internal air temp is relatively even throughout. The R-value of the combined system must be substantially greater than either component alone given my experience. I've successfully slept in a 30 degree bag with pad+UL7 on snow multiple nights inside a double-walled tent.

Edit: The weight of thin foam can be easily offset in shelter or sleeping bag weight reduction. Matt you are probably safe to assume that a more airy (lighter) shelter or lighter sleeping bag/quilt will be cozy once you pair your mat up with some foam given how warm you were sleeping without foam.

Had the same experience with my Big Agnes Q-Core SL this weekend. Went camping in about 20°F weather and the Q-Core was significantly transmitting the cold from the ground. I had brought a Z-Rest to top it with, as I had heard this might happen. I was glad I had it, it made all the difference.

Thanks all. There's seems to be a clear consensus to supplement the Synmat rather than swap it for the Downmat. I guess this makes sense as the added weight will come in lower than 105g, and the foam will protect the air mattress somewhat, and can be used for other purposes.

Anyone recommend a source for the 1/8" foam? I've seen it here http://gossamergear.com/sleeping/1-8.html, but the shipping to Australia is crazy.

You can get 1/4" foam at any Clark Rubber shop, in the form of very cheap camping mats. They may or may not have thinner foam.
I imagine you could get such mats at places like K-mart, Target etc, and at tourist camping places like Kellys as well.
Note that there are light foams and heavy foams. Check carefully. Do not buy open cell foam though: it will not work! Only Closed Cell Foam (CCF).

Cheers

Thanks Roger.

+1 on the 1/8th ccf. Used my synmat UL7 for the 1st time, probably got to 40*f, and was cool all over. (I run cold!) Added my GG thinlight and ahhhh, made all the difference.
Kelly

I have a local foam and rubber shop (http://www.actfoam.com.au/) that sells CCF in all sorts of ticknesses from 6mm or less to 10-15mm. Not sure how it compares to the supposedly very good Evazote stuff from GG and other places but I'm sure it's not very different.

Btw I have also been considering the Synmat vs. Downmat option. I had settled on a Downmat but now I think Synmat + 4-5mm foam might be the better more versatile option too.

EDIT: Btw, Exped themselves sell a 4mm Evazote mat which weighs 390g for 2000x1000x4mm. If they import it you could cut that down to 1000x500x4 for roughly 100g. I might go to my local Exped stockist and investigate this option myself.

Glad to hear Kelly G that I'm not the only cold fish out there!

Jeremy, I've got a quote for a 2m x 1m sheet of blue EVA30 at 3mm thickness from these guys: http://www.kangarubber.com.au/eva.html. $35 including postage. From my calculations this seems to be a very similar material to the Gossamer Gear Thinlight Pad (http://gossamergear.com/sleeping/1-8.html).

I've also found that arts and craft suppliers stock A4 and A3 EVA sheets at 2 to 3mm thickness, for only a dollar or two. For example, http://www.artworxgeelong.com.au/store/store.php?Eva_Foam_Sheets-pg1-cid265.html

Higher density and hence more weight, but cheap!

Density is the thing though isn't it. If we are talking about maximum weight savings then the GG pads still win, 82g for 1500x500x3mm. Logically, it seems that less dense EVA should be warmer too since it would contain more air, but I'm sure it's more complicated than that.

What's the difference between their EVA30 and the EVA75? And is that stuff Evazote? The black EVA75 looks like it could be…

Jeremy, I don't think it's Evazote. But for me I don't think that's a deal breaker. Couple of useful threads:

http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/5464/index.html

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=27718

I also read (but can't find again) a thread in which someone was saying they got a sheet of 3mm EVA foam (not Evazote), but the thickness wasn't uniform. Something to watch out for I guess.

Yes I suppose the difference in R values is not huge, but if I don't get it I'll always want it ;). I might see what this local guy has got in the 3-4mm range and see how that performs as it gets colder.

It definitely seems to be the case that the extra insulation added by thin CCF layers is not as simple at simply adding R-values, so a +/- 10% difference in insulation value probably isn't going to make a noticeable difference, all other factors being equal.

> What's the difference between their EVA30 and the EVA75?
A LOT!
The number is the density of the stuff in kg/cu-m. So EVA30 is 30 kg for 1 cubic metre, while EVA75 is 75 kg. Yep, big difference!

Cheers

I guessed that was the case. And I think the Evazote used in GG pads seems to be around 45 or 50. Gives me more info to go looker for similar stuff.