Why was I cold?

while you may have not seemed hungry or thirsty, slight dehydration and that the granola bars probably had under 500 calories are probably the culprits. When you go to bed, your body starts restoring the glycogen lost in muscles during the days activities. I would imagine most of the carbs went to that while any protein you had in those granola bars (very little if typical) went to rebuilding muscle tissue. that leaves little to no food calories to sustain metabolism and heat production.

A few other factors come to mind:
Humidity – higher humidity at low temps always seems colder to me (a desert dweller) than low humidity at the same temp
Time between dinner and bed and quantity eaten – going to bed hungry or several hours after dinner seems to make for a colder night, all other parametrics being equal
Mental state – *it seems* that when we take a group on an outing, those that are in fear of the bear, dark, the boogie man or whatever seem to sleep colder, albeit an observation and highly unscientific comment

You didn't mention what parts of you were cold.
Not sure if that helps,
MikeB

Another factor *could* be whether you had enough rest before starting the trip.

Blocking the vents of the tent could also have allowed more humidity to build up in the tent. I agree with Mike that more humidity will make temperature feel more extreme (both cold and hot).

Hard to say why exactly. I have been very comfortable with a nearly identical setup to temps at least 20 degrees lower.

One thought – the lining fabric on the Hydrogen feels cool to the touch on bare skin. I typically wear a longsleave base layer of merino wool top and bottoms, even in the summer. Not wearing anything on your legs could have given you a chilly feeling. Added benefit of wearing the base layers is keeping some dirt and oil from your skin from soiling the lining.

Crawling into the bag chilled can leave me with a cold feeling for quite some time. So some jumping jacks or running in place until you're warm before crawling in could help (you didn't mention your condition before turning in).

> I started out with the Wool 2 and R 0.5 top, then added the hat, then the Montbell jacket, and then was able to sleep. I swapped my dinner (chili mac) with lunch (2 granola snack bars), but wasn't hungry or thirsty when I went to bed. I'm just baffled that I felt cold at all.

Your gear does not seem the problem to me.
I strongly suspect you simply did not have enough dinner. 2 Granola bars???? Grossly inadequate!

"I strongly suspect you simply did not have enough dinner"

Most likely – I have pushed a hydrogen much lower then that – with just a base layer. With that set up, you should have been able to dip pretty low.

Simon, I can not be sure about your situation of course, but I learned the hard way that you need to insulate all areas of the body, preferably starting with an equalized base layer of say.. wool 2. I suffered a permanent injury called chilblains on my legs due to never insulating them well on some very cold field exercises. Despite having a warm torso I was loosing the heat as soon as the blood circulated the heat to my legs, like a cooling radiator. Of course, having only cotton/nomex at the time did not help either. Anyway, next time layer evenly all body zones. My 2 cents.
As other posters have mentioned, a warm calorie-rich meal before bed helps too.

For any time but dead summer:

If I don't bring my under layer of wool blend long johns I just never warm up at night. That layer makes me warm all over.
Hat.
Long sleeve shirt on.
I carry a think pair of socks for bed (wool liners). It is worth the weight.
A hot beverage in the hour before bed. Yes, I'll have to pee..but oh well.
A good meal earlier and a snack before bed of high fat/calories.

If I get really cold (and I do) I will drape my down jacket or vest over my torso inside my bag. This usually warms up my butt/back and upper legs.

I sleep in a 15* usually, so take my advice at your own risk ;-)

This isn't scientific but I have noticed over the past couple years:
Don't wear a down or similar jacket to bed. If you need the extra insulation, drape it over you, under your sleeping bag. It allows the air to warm up better and you don't crush the insulation.

Oh yeah, and gloves. I wear liners to bed often.

I would add my vote to you not having enough food / water. This can have a dramatic effect.

On a group trip several years ago I didn't get enough food for dinner and most likely not enough water. I ended up going to bed early because in the 50F conditions my thermawrap vest wasn't keeping me warm enough… normally base + hat + vest + windshirt keeps me good to 25-30F. I got under the quilt and found I needed to use both the quilt and my vest to stay warm enough to sleep. The low that night was something like 45F. Normally I can use the quilt without the vest to 30F, and have been warm enough with the vest + quilt down to around 15F.

–mark

I agree with the majority. Eat better and, like Sarbar said, "A hot beverage in the hour before bed."
I would add that after you warm your body by some exercise, as mentioned by Jason, and that hot beverage, pour some more of that hot beverage or water into a Nalgene (actually, I use a Platypus) and tuck it into your bag with you, around the crotch region.
It works for me in really cold temps.

Really great advice, thanks everyone!

Mike B: My legs were slightly cold. My torso was the coldest. Hands and feet were fine.

Pam suggested humidity–yes, the humidity outside was high (80-90%, from records), leading to a damp sensation (which was driven by the wind).

I swapped lunch with dinner on a (now) foolish lark to 1) save cooking /cleanup time in camp, and 2) keep the smell of cooking/food off my clothes prior to bedding down as I was going to be in camp for 5 hours before bedtime (and there are bears, oh my!). I did not feel hungry ever that night, and wasn't even interested in breakfast (although I was hungry after I finished preparing it). With 20-20 hindsight, I agree diet was the no. 1 cause.

Next time I will use a baselayer on my legs (which I usually bring but eliminated to save 5.8 oz.-doh!), and follow the meal advice. Hey, I love to eat!

No one mentioned conductive heat loss thru the BA pad. At times the ground thru the pad felt cold. Just a sensation because of the low metabolism?

The last time I had mine out in cold temps (prob. high 30s in the Sierra) I felt I was losing heat through it, and had trouble getting warm even with my R0.5 longjohns, LW smartwool top, beanie, nunatak arc alpinist and cocoon pullover (both draped and worn at various times). Had a big dinner but not right before bed.

A couple years ago there was a discussion on these forums of the relative contributions of conductive, convective and radiative heat loss in sleeping situations, and the take-away conclusion was that ground conduction was a large component of heat loss even in relatively mild conditions. As a result, the insulating ability of the pad is an important contributor to a warm night's sleep even in non-snow-camping situations where you might not worry about it. Don't have time to look it up but it should be in the forums still somewhere.

In a comparison of R-values of various pads I saw around the same time, the BA Insulated Aircore was pretty low, despite the "insulation." I think I recall a more recent table around here lately. Primaloft is more vulnerable than PG or down to the repeated (fairly dramatic) compression that a airmat filling will undergo. And early models of this pad had a problem with the insulation delaminating in strips, which I believe was fixed.

As a result, I switched to taking a NightLight for any reasonably chilly weather. Now if I could just get the same comfort . . . I've been toying with the idea of combining the BA Insulated Aircore with a 1/8" thinlight for the best of both worlds but haven't tried it yet. Of course, the R-value of the down airmats is great. Maybe that's the answer . . . Santa are you listening?

"Of course, the R-value of the down airmats is great. Maybe that's the answer . . . Santa are you listening?"
Ho-Ho-Ho!!!……….. (Well, you wish anyway)
My Exped downmat 9 has an r-value of 8.0 and weighs a hair over 2 lbs. I know, heavy. But I will gladly cut almost anything but food and water to accommodate it.

> No one mentioned conductive heat loss thru the BA pad. At
> times the ground thru the pad felt cold.

Hmm… If you were feeling cool through the pad then it wasn't providing enough insulation and that could be as much of a problem as not having enough fuel. Either you need a lot more insulation that me, or maybe your BA pad is having troubles. Could be that your primaloft is compressed, insulation it no longer bound to the top of your pad (this was a problem with the first pads shipped), or you were using the pad insulation side down.

50-55F is where I start to noticing cold ground when I am using an uninsulated air mat. I have used the BA Insulation air core below 30F without noticing cold. I use a quilt… the only thing between me and the pad is a medium weight base.

–Mark

How long was the original poster using the BA pad?

So that pad must be used with a certain side up for proper insulation since the insulation is only on one side?

At least with the older BA pads the insulation is bonded to the top of the pad which has the logo on it. I find this useful. In the summer I flip the pad over which help me not overheat at night.

"How long was the original poster using the BA pad?"

Just one night, if that's what you're asking.

"If you were feeling cool through the pad then it wasn't providing enough insulation… Could be that… you were using the pad insulation side down."

I can't remember for sure, but I usually keep the logo facing up. But it does beg the question, "Did I or didn't I?"

"At least with the older BA pads the insulation is bonded to the top of the pad…"

Mine was purchased in March 2005 from REI (is that an older pad?). I kept the Air Core mostly unrolled (but deflated) with the valve open. But now I'm beginning to wonder if it should have a few puffs of air to protect the Primaloft.

I had a similar problem and found that the insulation was coming off. Inflate and hold up to the light and look for differences. BA exchanged mine free of charge. I do believe the logo side should be up for insulating.