When having to spend a night outdoors whether it be during a back packing trip or during an emergency it is of utmost importance to keep the bodies core temperature at 98.6. Remember the golden rule: 3 Minutes without air, 3 hours without shelter, 3 days without water and 3 weeks without food. Next to oxygen, shelter is a priority. As soon as your core temperature dips below 98.6 the clock begins to tick and it becomes an equation of physiology versus time, but it is an equation and there’s nothing you can do to stop the equation other than getting your core temp back to normal. The best way to prevent this is to not have your core be compromised in the first place. The simplest way is to have a warm bed to wrap yourself in. There are a number of sleep systems you can choose from and I’ll highlight several.
Sleeping bags can be made into two separate categories, Down and Synthetic. In the two categories there are a couple shapes you can get. There are Mummy, Rectangular and Semi Rectangular which is somewhat new to the market place. The Mummy bag will most likely keep you warmest because it has the tightest fit and has a hood with a drawstring which can be cinched tightly over your head to the point where only your mouth and nose are exposed to the elements. Some people with claustrophobia issues do not like mummy bags but I strongly recommend a mummy bag because you can alway sleep with the bag in it’s most open configuration and if you get cold make it tighter, but with a rectangular bag you only have one option. The semi rectangular bag solves some of the issues by making a roomier bag around the shoulders and hips but still have a hooded section.
Here’s what the shapes look like:
Synthetic bags are inexpensive, heavy and don’t pack down as small as down, but when they get wet they’ll still keep you warm.
Down bags are lighter, warmer, more expensive and last longer but they loose their insulating value when they become wet.
The newest type of sleep system on the market are the ultralight Quilts. The theory is this: when sleeping the material on the bottom of the bag compresses so much that it becomes useless, so if you are trying to be an ultralight hiker why carry weight which doesn’t do you any good. Strip away the bottom of the bag and use your sleeping pad as your insulator. I have not slept in one of these bags but I can tell you that the slightest draft wakes me up so I’m not sure I’d want to sacrifice the extra 4-6 ounces the bottom of my bag costs me. None the less this is a viable option for those who want the smallest lightest sleep system. Just know you may be risking the 98.6 rule.
The greatest heat loss is between your body and the ground. You need a layer which will stop the sucking of your body heat into the Earth. When the sun goes down the Earth becomes a refrigerator and it wants to steal every BTU of energy your body has, to counteract this there are several choices you can make.
The inflatable mattress is a great way to not only create an insulating layer, but add a little comfort. I like the old school Thermarest. I think I have version one, it’s at least 20 years old and it’s still functioning perfectly. It’s rectangular weighs a lot and is very comfy.
For a while I tried to use a lighter weight Thermarest pad but in the end I found it too thin, not as comfortable and it slid around way more than my old school pad. I had bought one that only went down to my hips and I became too cold on my legs during the night so I went back to my full sized pad and chose to hump the extra 4 ounces.
TIP: To prevent sliding around on your pad in the middle of the night use silicone on your sleeping pad to create friction strips.
Beyond the smaller Theremarest is a skeleton pad which is supposed to only give you support in the areas you really need it, head, shoulders and hips. The open areas are supposed to create thermal pockets to generate warm air… I have my doubts about this type of sleeping pad. A bad nights sleep is simply not worth the savings in weight. Having said this there’s plenty of through hikers doing the PCT who would argue that this savings of weight is way more important.
Another style I have used is the Closed Cel Foam pad below is an accordion style egg crate mattress. It is a very lightweight low tech way of creating warmth and comfort. The egg crate gaps create pockets where air is trapped and become warm. The down side is it’s a little bulky and you usually have to strap them onto the back of your pack. When doing extreme hikes the pad on the outside of your pack is usually the first casualty due to branches and sticks ripping it apart.
Closed cel foam pads are also available in a simpler and cheaper version, basically a thicker Yoga mat:
Chairs are also a good sleeping pad, simply they’re just a sleeping pad with two buckles which allow them to be affixed to a 90 degree orientation. Of course now knowing this, all you have to do is take your sleeping pad and wrap either a length of cordage or a piece of webbing around your back and under your legs to create the same thing.
Hammocks are a pretty cool way of having a lightweight shelter but there are a few factors you have to keep in mind. One, you need two objects to suspend the hammock from. Two, even though you are off the ground you are exposed to the elements and it can get cold so a modified sleeping pad may be required. Three, if you are a stomach sleeper the hammock may be uncomfortable. Four, by the time you add up the hammock, the bug net and the tarp the weight comes out to almost double what my tent weighs. With this in mind the hammock packs way smaller in a backpack and if you have a poncho then you don’t need a tarp like the one below. If you have a head net for bugs then you don’t need a full bug net for the entire hammock so you can save weight if you’re truly going for a survival style hammock.
I love the design of the Jack’s R Better hammock, they suspend the entire hammock from the top allowing a person to sleep in any way they want. It’s also a very stable platform.
Here’s an example of a modified sleeping pad for a hammock in cold weather.
This is the Jack’s R Better solution for cold weather in a hammock, put the down on the outside of the hammock creating a very big thermal break between you and the elements… Obviously there could be issues in wet weather. I don’t know of a workaround to this problem because it seems even with a tarp if there’s a little bit of wind the spray could get the down comforter wet.
Now, having said all this what is best for your 72 Hour Bag? Well there’s one more option I’d like to give you. SOL Provides a variety of emergency sleeping products like the Emergency Blanket pictured below which sells for about $4.95 at REI:
Moving up on the comfort scale is the Emergency Bivy which is basically a sleeping bag without any insulation other than the mylar coating on the inside designed to reflect your body heat back in to you. It sells for $16.95 at REI.
The next step is the Thermal Bivy which costs $29.95 at REI and has four layers to trap your bodies heat. It claims to reflect 80% of your body heat back in to you. It claims to be so warm there’s a vent in the foot box to prevent you from getting too hot.
Lastly, the grand daddy of all the emergency bivy’s sold by SOL is the Escape Bivy for $50 at REI. The bivy’s above can create moisture in the bag from you perspiring but this last on is Breathable allowing moisture out and still able to keep the heat in. This is the one I carry in my 72 Hour Bag. I feel it’s the perfect balance between weight/size, money and warmth.
I don’t pack a thermal pad in my 72 Hour Bag, because I don’t want to take up that amount of space in a bag which needs to be as small and efficient as possible. But I know what needs to be accomplished in the field to achieve the same thing. I carry an edged tool and one of it’s purposes is to cut branches and leaves to get my body off the ground. Knowing what’s you need to do and having the concept in mind will allow you to improvise when the time is needed. Knowing where to cut back and save weight is also a valuable factor in preparedness,