Is it the same to stay warm, if you skip out on a sleeping mat, and just use a lower temperature rated sleeping bag?

I have an airbed with no insulation...

In the summer, when the ground and air temperatures are comparatively warm, there is no great need for insulation underneath you.

When the ground is cold or the air temperature is cold, you do need effective insulation beneath you to stay warm. Most sleeping bags do not do a good job of insulating beneath you because the insulation, whether goose down or synthetic, is compacted by your weight and loses effectiveness. A warmer rated bag will help very little to insulate you from the cold below.

Various foam pads or insulated air pads are necessary in cold weather. Check out their 'R' rating to discover how well they insulate.

I guess you are saying, that I will feel cold spots where I touch the ground (or not touch the ground, with the airbed), even if I have a zero degree sleeping bag, in 30 degree weather.

First of all, I'm no expert, but I have read a lot about this subject and spent enough time in a sleeping bag to have a basic understanding of how all this works.

So the answer to your question is well, perhaps not, but very likely. But, an air bed is not the same as insulation like a pad, unless the air bed itself has some kind of insulation, which let's assume yours doesn't.

Pads and bags serve two different functions. A pad (not an airbed) cushions you from the hard ground and insulates you from whatever temperature the ground may be. Bags insulate you from the surrounding air and keep air that is warmed by your body heat in the bag. Some people use quilts based on the premise that because your body weight crushes the insulation under you (meaning the down or synthetic batts in the bag, it is ineffective. This makes sense, but if you use a quilt, you will still need a pad.

The air in an uninsulated air bed will be the same temperature as the surrounding air once it has been filled for a while. It may be comfortable, but it won't be warm without a pad of some sort on top of it. People who use hammocks often use pads in the hammock or an "under quilt" of some sort that is actually fastened under the hammock to keep them warm.

The biology and physics of how you stay warm is fairly complex. Most of us learn the basics by reading or asking questions, or by experience-getting cold and figuring out why.

Don't believe everything you read. Here is an example from the website eHow.com, supposedly written by an expert - Backpack sleeping bags are designed so that their insulating fill-material captures and stores a hiker's body heat.
THIS IS NONSENSE. TOTALLY UNTRUE.

That is not how a sleeping bag works. If this was true, your clothes would be hot when you take them off. They might slightly warm be for a brief time, but certainly not body temperature and not for long in cold weather. It works by separating you from the ambient air outside the bag; the more separation, the warmer the bag. It is the same principle behind the wetsuit-it traps water warmed by your body and separates you from the cold water outside the suit. Same idea, different medium.

If you want to know more, read this-
Article on staying warm

The author of this article seems to have a pretty good handle on what your body is doing and how to stay warm, based on what I know.

I read this morning in another thread, that you could put the airbed inside the sleeping bag. Then my body would heat up the airbed-sleeping-pad, and I wouldn't have cold spots, but the inside of the sleeping bag would be colder overall, due to heat loss to the ground.
In any case, I decided to get an insulated airbed-sleeping-pad, because my sleeping bag isn't warm enough to try sticking the airbed-sleeping-pad inside it. Not to mention, I may not be able to curl up so easily... even if the klymit static V may be somewhat flexible?
http://www.klymit.com/static-v.html

I use a piece of "Reflectix" under my bag when it's cold out. Using a piece of this under an air mattress will provide some insulation from the cold ground and help keep your mattress warmer and bag warmer.

A piece of Reflectix cost a lot less than an insulated air pad and it's pretty lightweight, so it's a good option to consider.

The most basic problem in cold weather is that both the ground and the air are excellent heat sinks, in other words, heat will tend to conduct away from your warm body and into the ground or the air until their temperatures are equal, which they will never be, because the earth and air are much too big for you to warm up, so the reality is that your body must constantly resist cooling down to their temperature. Insulation doesn't stop this cooling process; it only slows it down to what is (you hope) an acceptable level that your body heat can keep up with.

Compared to the air in your mattress, the foam insulation in a foam pad is a very poor conductor of heat. An air mattress with no insulation puts very little conductive resistance between you and the air inside the mattress. The air in the mattress will quickly and efficiently conduct whatever bit of heat it contains directly into the ground, so no matter how much heat goes from your body into the air mattress, it will soon be conducted away, almost as rapidly as if you were sleeping directly on the ground.

The problem with thinking in terms of a few "cold spots" is that those cold spots are not static things. They are places where heat is actively being sucked out of your body. Your body will attempt to cut this loss by reducing blood flow to those spots, but there is a limit to that, since those cells need blood to stay alive. Eventually, your body will fight the cold loss by forcing you to exercise and burn calories more quickly to generate heat faster. That exercise is called "shivering".

Totally unscientific but I have never been so cold as sleeping on my daughter's blow-up guest bed without an insulating under layer. Although it was only 68 degrees in the room it sucked all my heat up. A foam pad works well if you do not mind a hard surface; a blow-up pad with insulation is softer and protects from lumpy ground, but generally heavier and a lot more expensive.

Two times I have been really cold! The first, similar to W_D's experience, was on a blow-up air mattress on the concrete slab floor of my eldest son's apartment at the time, even though the slab was carpeted and the air in the room well-heated (this was over the Christmas holidays). I moved to the sofa for the rest of my visit.

The other was an 18*F night at 5,000 feet in the Washington Cascades on an early NeoAir, used with a 1/8" closed cell foam pad. My Western Mountaineering Ultralite kept me cozy warm on top, but I was shivering uncontrollably underneath! There was definitely not enough insulation underneath!

Get that insulated air pad--it's worth every penny! If you can't afford it, get a fairly thick CCF pad. While the squashed portion of your sleeping bag that is under your body is not, as some claim, completely devoid of insulation, it has far less than the portion on top of your body. You can tell by measuring the thickness of the sleeping bag that's squashed under you vs. the thickness of what's on top

I tried a non-insulated air pad once, thinking it would be fine for warm nights. I started getting cold underneath when the temp got down to the upper 40's F!

LIke OM and Daisy, the only time I got cold was on a floor in a heated house on an uninsulated air bed - and I had a blanket below me, on the air bed, as well as over me.

You seem to be asking several times if you can get away without an insulated pad. The answer is an unequivocal no, even in the summer. (You don't need as high an r-value, but you still need something, in my opinion - the only exception is if you are sleeping on solid rock slabs that have been heated by direct sunlight all day in August.)

You need insulation under you. If you sleep on the ground, you need an insulated pad; it can be 48 inches long, with your pack under your legs, if you like, but you still need it. I'd recommend an r3 for summer, and r5 for winter, in the Ohio River valley. If you hammock, you can use a closed-cell foam pad inside the hammock or an underquilt (down or synthetic) hung under the hammock so your body weight doesn't compress it.

Sorry if this comes across as too blunt or rude; not my intent. I just wanted to be unequivocal in my opinion.

The coldest bed I've slept in was a water bed with no heater. Those will sure suck the heat out of you. I was young and dumb back then, so I just kept sleeping on it.

I agree that you need a good pad, but I'd still get and use the Reflectix.

Just a few months ago I forgot my pad and slept on a piece on the ground. It was chilly, and hard and lumpy too, but I stayed warm enough.

Reflectix has no "R-Value", so how and why it works is sometimes misunderstood, but even when compressed the insulation in your bag provides the air space needed to retain warmth from the reflective material (as do the bubbles in the Reflectix material itself). I won't go into that anymore here, but I think it has a lot of qualities that make it a very good option for our usage.

I've spent a few nights in the 15º to 40º F temp range over the past few years and for me a piece of Reflectix has become essential gear. It can be the difference between being cold or not and any pad and bag can benefit from it (even the pad you forget).

Bill, I missed your post about Reflectix when I wrote. I think the basic point I was making would apply equally to Reflectix: it would count as insulation. I don't know much about that material, but I assume it might be like a space blanket on steroids? Or, more accurately, it might work more like the stuff inside the NeoAir pads, which (rather than trapping warm air and keeping it from moving around inside the pad) also reflects heat back toward you?

I chose the r-value examples because it's what I'm familiar with, but the overall point is that you need insulation, not just air, under you.

Bill, you are so right. I have been sleeping on water beds for years (very old school) and depending on the design, if the heater goes dead, it will suck the heat right out of you, as you said.

I use two pads on snow - a Therm-a-Rest full pad (one of the older ones) and a Ridgerest closed cell pad that I stack on top of the inflated pad. That seems to work best rather than the other way around. The Ridgerest separates me from the air in the Therm-a-Rest.

Exped and Stephenson make down filled pads. I think there are other brands as well. I have read that the Exped may develop leaks over time, so I would take a repair kit if I got one.

I just got the Exped UL7 Downmat (the lighter version) and will let you know if anything happens to it. A couple of nights on the floor have been quite comfortable. In fact, at its first trial when I had planned to lie on it for only a few minutes, I fell asleep and woke up three hours later!

My main beef is the two heavy valves in it, which are incompatible with any pump except their "Schnozzle," which also has a heavy valve. And why two valves (separate for air in and air out) on the pad? Of course you can't blow up a down-insulated mat by mouth (result is soggy, non-insulating down). The required Schnozzle adds 2.3 oz. to the weight of the pad, and because of Exped's unique valve, nothing else will work (no Instaflator or plastic garbage bag). The Schozzle is waterproof (I tested it), so can be used as a partial pack liner or a dry bag for your sleeping bag. It weighs more than twice as much as the dry bag I have been using for my sleeping bag, though.

At least the weights in the specs agree exactly with the weight on my postage scale. 17.8 oz. for the mat, 2.3 oz. for the Schnozzle, 0.4 oz. for the repair kit and 0.5 oz. for the stuff sack. Since I have a pad pocket in my pack, the stuff sack won't get used. 20.5 oz. for the total without the stuff sack. That's for a 64" long mat (which, for me, is full length). Not too bad since my old POE Insulmat Max Thermo weighs just under 17 oz. by itself and is only 48" long. I'm sure that Exped's weird valves add a couple of ounces to the pad and an ounce to the Schnozzle!

It doesn't seem any more fragile than my 7-year old POE pad, and less so than my slip-and-slide Kooka Bay pad. It also is less slippery than either.

It will take a few nights in the field before I am positive that this thing is a keeper, but so far it is certainly comfortable! From indications so far, I'm willing to overlook the unnecessary extra weight. I really like the outer tubes in the pad being slightly wider, keeping me from rolling off!

Slightly less pricey thanks to the REI 20% off coupon and a small dividend. Still not cheap, though!

Last year I got the Exped synmat ul7 and have spent 10 nights one trip and 3 nights on another and so far I love it. Mine didn't come with the snozzel so I have to blow it up but that's not a big deal. I still worry about long term use. I could see if it got a leak half way through a 2 week trip could be bad.( if I couldn't find the leak in the field)

Thanks to all for this discussion! The airbed I have been using is a big agnes air core, R=1. I did get the Klymit Insulated Static V. It's not the lightest, but it should keep me warm. If I had read this earlier, I would have tried the Reflectix first. At home depot, you have to buy a huge roll. Maybe this: http://www.ebay.com/itm/Emergency-MYLAR-...=item3a8ce1095a
I imagine it doesn't do much for conduction, but takes care of heat loss through radiation: http://en.wikipedia.org/wiki/Heat_transfer#Radiation

Reflectix R value:
http://reflectixinc.com/basepage.asp?PageName=What+About+R-values%3F&PageIndex=389
Um... does this mean that, combining reflectix with a big agnes air core with R=1, you would have R=2.1? Does the R value include heat loss due to radiation, and how much is lost due to radiation anyway? My first thought was that radiation heat loss is pretty negligible (only worth considering with huge temperature differences). However: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2844235/

http://general.utpb.edu/FAC/eldridge_j/KINE6362/unit4_l1.html "Although the greatest amount of heat loss from the body at rest occurs through radiation..."

However, I think these statements are about heat loss to the air, while standing. Conduction is probably a bigger factor laying on the ground. I wish I had some percentages.

Doesn't give any specifics, but nonetheless informative as an intro: http://www.trailsherpa.com/blog/2013/03/19/the-science-of-sleeping-bag-design/

Yeah, you can add the R value of the Reflectix to your pad.

In both of those I suspect it's really the trapped air space and plastic that provides most of the R value.

But it's not the R value that provides the most benefit with Refelctix, it's the reduction in radiant heat loss.

To really get a feel for how it works you should get one of those cheap "emergency blankets" and play with it. They have no R value but they're great at reflecting radiant heat.

You'll find that when the emergency blanket touches your skin it becomes a quite nice heat conductor and helps the cold air on the other side suck the heat right out of you.

That's not exactly what you'd expect, and probably why most people aren't impressed with them.

If you experiment a little further and trap a thin layer of air between your skin and the emergency blanket it starts reflecting the radiant heat from your skin and heating that air instantly (wool or fleece traps air nicely for this purpose). With that small change it works like intended and you can quickly feel the warmth it traps, and done right it's quite impressive.

Reflectix has a built-in layer of trapped air. Used under your mat it will warm the air in the mat first and most. Used on top of your mat it will warm the air in your bag first and most.

Like any piece of gear, you have to practice a little using it to get the most out of it.

For the sake of experimentation :), I ordered a mylar sleeping bag, and will put the big agnes air core inside of it. I may turn it inside out, if that is necessary.

What are you talking about? One of those survival bags? If so, not my idea of a good night's sleep.

What Tom you don't like being soaking wet and mildly hypothermic?

A buddy of mine got one of these this year and used it on a trip we did. He said he woke up cold and put inside his sleeping bag and was nice and warm afterwards.

Warning--by morning this setup will be a sauna inside and any clothing you wear inside will be soggy in the morning. That's because your body moisture ("insensible perspiration") will have nowhere to go during the night.

If it's below freezing, this setup, in essence a vapor barrier, may be OK, as long as you don't wear anything but a base layer inside the mylar bag.

I ordered a mylar sleeping bag, and will put the big agnes air core inside of it.

I think many people commenting here failed to notice that mekineer intends to put his sleeping pad into the mylar bag, not his sleeping bag. This seems like an interesting experiment that might reduce heat loss from underneath him through the night.

For the past 2 years I've been using a SOL E-blanket that looks exactly like that bag on the floor of my tent in the winter. I believe it's helped prevent the snow melt damp spots you usually get and that we had much less problem losing heat to the ground.
It works especially well if I wrapped it around our pads instead of just putting it on the floor of the tent. I have used Reflectix in the past, works great, just a little more bulky. The pieces I had were trashed. I used them as seat pads ice fishing. If I end up buying some for a job, I'll steal some to use in conjunction with our Neo-air pads. I think Bill S. has outlined using both the mylar blankets and the radiant insulation in his winter shelters. Stuff works.