The three key factors to keep in mind when sleeping in the wilderness

After years of camping and spending as much time as possible in the outdoors, I can say that knowledge to sleep under the stars requires a certain learning curve. It doesn’t matter if you camp in good or bad weather, if you are doing it for pleasure or in an emergency, there are always three key factors you need to consider.

These three variables are well-known by experienced campers and are always considered when establishing their shelters. I learned about their importance a while ago by using the “IOU” acronym, which stands for Inside, Over, and Under.

I first learned about this concept from Ray Mears, a survival and bushcraft expert who presented it in his books. This principle applies to everyone, regardless if you are an outdoor enthusiast, a survivalist, or a prepper, and mastering it will make sure you build a proper shelter in any environment you can possibly imagine.  

The principle follows the common-sense rules of shelter building and includes something to sleep in (the I), something to sleep over (the O), and lastly, something to sleep under (the U). This, of course, will depend on the environment and will be dictated by the scenario you are facing. It goes without saying that every climate has its own challenges, but even so, you can address these various challenges by following these three variables.

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When discussing this variable, most people will assume that it refers to a shelter (natural or man-made), but that’s actually the second layer. The first line of defense against the cold and the elements are actually your clothes. You should have enough clothes to spend at least 24 hours outdoors, dry and warm.

Your clothing needs to be modular because you should be able to sleep and work in your clothes without problems. Depending on your level of activity and the elements, you should be able to peel off or add a layer as needed.

Your clothes will get wet and dirty and won’t insulate your body efficiently, resulting in failure to regulate your body’s core temperature. While you should have a set of clothing for sleeping, you also have to consider a second insulation layer. This may be a sleeping bag, quilt, tent, or natural shelter. When you lack man-made items to sleep inside, you should consider using natural insulation or various fire-heating methods.

What it’s also important to mention here is that what you choose to sleep inside can often depend on various factors. For example, packing something to sleep inside requires backpacking room, and you need to make sure what you’ve packed is ideal for your environment. Another example would be a scenario in which the “sleeping inside” factor is planned for, or perhaps it’s an emergency situation in which you have to make do with what’s available.

You need to match the insulation layers to your environment, and you must make sure it stays dry, free of tears and that you have enough space to carry those insulation layers. Also, check that they are rated for the appropriate temperature because it would make no sense to get a summer tent if it’s snowing outside.

If you are forced to improvise using natural resources, you shouldn’t overlook materials such as dried leaves, grasses, needles, and others since these can be used as an extra insulation layer with your current setup by layering them on top of it.

A trash bag, for example, it’s lightweight and doesn’t take much room in your backpack. You can use it for material collection and improvise a mattress or insulation layer, or you can use it to keep your clothes dry.

Regarding the things you pick to sleep inside, you shouldn’t forget about a protection layer that will keep you safe from insects and other critters that want to feast on you. For example, a hammock has insect netting, and such a layer can be improvised for other sleeping items as well.

Another thing worth mentioning is that you have to maintain your shelter each morning by adding additional insulation where it was worn or matted down. Also, don’t forget to aerate and dry your clothes in the sun or around a fire.

You should never assume that your outdoor “expedition” will last as expected, and each day you should work on improving your shelter to make it stronger and more durable with whatever items you can gather or repurpose.


The layers we mentioned above will protect you from the cold environment around you, but they won’t do a good job of separating your body from the ground beneath you. Heat transfer occurs when a warm surface touches a cold one, and in this case, your body, sleeping bag, or clothing will transfer heat to the ground beneath you.

This is often the main cause of hypothermia, even if you find yourself in a warm environment. You need to create a dead-air space to sleep over to prevent your body from losing heat and succumbing to hypothermia.

If you planned for this trip, you’ve probably packed a closed-cell pad or some type of inflating pad to keep you off the ground. In some environments where the ground is unhospitable, bringing a hammock is ideal since it lets you sleep over damp ground, uneven terrain, and even sharp rocks.

In an emergency, what you sleep over requires a great deal of improvisation, and it will help you survive the cold night. The trash bag we mentioned can come to your aid in this scenario since you can fill it with fluffy debris and use it as a beanbag chair. If you have a tarp, you can place it on the ground to create a waterproof shield and prevent your clothing from soaking up moisture if the ground is wet.

If you have the tools, you can build a raised bed from logs and use a poncho or a tarp as a wind insulator. This is usually recommended in a winter scenario when you have to make an effort to keep your body above the icy ground. 

If you do find yourself in an environment with dry and cold ground, you can improvise a hot bed by digging a hole (the length of your body) and filling it with heated rocks or coal. Add a small layer of dirt over the heated material, and you can sleep directly on the ground. However, you need to pay attention since there are some risks involved. For example, heating porous rocks with water trapped inside can cause them to explode, and you may get injured. Also, speaking of injuries, you must make sure the heated rocks or coals are completely buried since you don’t want to roll over and wake up with a burn or light up your sleeping pad or any other flammable materials.


Depending on the environment, you will probably need a roof over your head, and what is considered a roof may vary from one person to another. The tent you bring along will offer a roof over your head, and so will a tarp or a poncho. A camping hammock has a dedicated canopy that can protect you from falling bugs and the elements.

A roof will not only protect you from falling rain, but it can also act as an insulation layer, trapping the heat of your body depending on what it is made of. Even more, having a shelter with a roof can become a morale booster since you have a roof over your head, similar to back home.

There are all sorts of modern materials available on the market for campers and preppers, and leaving home without some emergency gear that can be used for improvising a roof, for me, is unacceptable. For example, an emergency blanket is lightweight and can be used to improvise a shelter or make a roof for a shelter you’ve built from natural materials. Carry some cordage as well and use it with the trash bags filled with grass and leaves to improvise a roof.

The shelter you build is not only your sleeping place but also the area where you live, so if you carry a 10-foot-by-10-foot tarp, you can use it to construct an A-frame or lean-to shelter with plenty of room for other activities as well.

Your shelter can be made from repurposed items, and your vehicle or a small cave can be converted into a proper shelter if you have the gear and resources at hand. In this case, the IOU factors are covered, and you will have to work less to improvise a shelter. Even sleeping under an overturned raft or canoe could be an option to create a shelter in the field.

If you are forced to work with only natural resources, you could look for natural shelters such as caves, downed trees, or a heavy evergreen cover as long as you make sure there are no inhabitants or build a shelter from available resources that would suit your needs. Take advantage of natural features and use your imagination.

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Stay busy and always improve your shelter

Never assume that your shelter is temporary or that you can’t do anything more to improve it. There’s always room for improvement regardless of what items you’re working it. While a broken-down car may cover the IOU variables, that doesn’t mean it’s the perfect shelter. For example, sleeping inside a sleeping bag in your car is much better than sleeping in your clothes in just the car’s dead air.

Remember to update your emergency or bug-out bag as the season changes because it contains items that can be useful all year long, and there are items that need to be replaced depending on the expected temperatures. Not to mention that some items may expire or get damaged if they are not properly maintained.

When sleeping in the wilderness is a planned action, you should also ask yourself if the IOU factors are covered and what you need to do to make sure you make your situation comfortable. The same goes if an emergency forces you to evacuate and you find yourself in an unhospitable environment. Ask yourself what you will sleep inside, over, and under. 

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