Why not naked: Sleep System

10 min readMay 9, 2020

This is a series of articles called Why Not Naked: outdoor gear advice and guides for those who plan to go out for a multi day hike. I know, there are gazillion of these out already, but maybe this one is just a tad different to provide additional insight.
Going outdoors is much about returning to the basics. To forego luxuries and obesities of our comfort-infested homes and for a short period enjoy the freedom of being streamlined, being stripped down to minimum, weighing every piece we wear, trading off weight for time outdoors, shaving off every non-essentials, asking existential gear questions to the point of asking … why not naked?

Topics:

Basics of heat transfer and heat generation
Multi-day Sleep System
Multi-day hiking Clothing
Multi-day hiking Boots & Socks

Basics of heat transfer

In order to understand sleeping gear better, one must understand the key underlaying problem: heat loss. So, first, let’s dive into physics a bit:

Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes (source: Wiki). Also our body looses heat by these 4 means:

Conduction, transfer of energy by touching : heating hands on hot stove, seating with your behind on cold marble stairs, sleeping lying on the floor. Cooling by touching ground is by far the fastest heat loss and thus the most important one.
Convection, transfer of energy by moving liquids or gasses: e.g. fanning your hair or wind chill. Air is gas and in gasses molecules can move around, taking heat with them. Your skin heats the air by conduction and then that air moves away and new, cooler air touches you, and you get cooler.
Radiation, transfer of energy by electromagnetic radiation. 5G deniers might be baffled, but our body radiates heat. Since we are much cooler than the sun, we don’t radiate much, and certainly we don’t glow. But we still lose considerably more heat by radiating than we think: this is why first aid kits include reflective folio.
Phase changes, transfer of energy by changing from liquid to gaseous form: When you sweat you enable droplets of water on your skin to evaporate — change phase change from liquid to gas. In this chemical process, energy is being used, which makes your skin end up cooler.

To prevent heat loss:

Prevent conduction Introduce a good amount of stuff between your body and materials that conduct heat well: this is called insulation. What conducts heat well? Stones, floor. What less? Wood, Air. As you can’t sleep floating in the air, you have to touch something, and this is your sleeping pad.
Prevent convection. Prevent air to move around you. Down sleeping bag traps about 10cm of air around your body and prevents it from moving and mixing in with environment. Tent does similar, but with much larger amount of air which mixes faster with environment.
Prevent radiation. introduce things around you that reflect radiation. Sleeping in a rescue foil is an overkill, but other materials, such as sleeping bag and clothes reflect radiation too.
Prevent phase changes. This one seems simple, just don’t sweat! However, being hot or not, your body evaporates a few deciliters of water overnight through your skin in any case. Arctic campers introduce vapor barriers into their sleeping bags, but for you it is enough to just make sure have a tent so you are not wet and that by any chance you are not sweating because you are too hot!

Basics of heat generation

Our bodies are generators of heat, stoves basically. By burning sugars from food, heat is released. This makes our body constantly hit that delicate sweet spot of 36.5 degrees, while average overall air temperature in our environment is around 22 degrees, which makes our environment cooler on average by about 14 degrees. You are constantly losing heat and your body is made in a way to compensate. But differences in air temperature are gigantic compared to our body temperature differences: I have experienced temperatures from -20 up to 50, probably. It is only possible to survive these differences because air has such low conductivity, because our skin enables us to prevent heat loss and releases heat when sweating, and because of insulating clothes … and we can help our body generate heat when we need to.

Care for heat. Insulation only prevents heat loss, it doesn’t generate it. Ovens, fires and other heat bodies generate heat, but these are very scarce outdoors and they need setting up, fuel and care. It is better to rely fully on insulation to prevent heat loss than on other heat generators than our own body.
Don’t lose it. If your body gets too cold, it will employ muscles to start shivering and burn calories in order to keep warm. At this point your body is already working hard to get back that heat, you are a bit too late, and you are losing energy you need for hiking. This is why it is better to prevent getting cool in the first place. Act early to prevent heat loss and don’t rely on shivers to tell you the bad news.
Get it back. If you got cold it is not enough to just prevent heat loss by dressing more, but it is important to generate heat by moving muscles or eating. If you are cold you might will not get warm immediately when you jump into your sleeping bag. Make a few squats or jumps, exercise with your limbs, to make your blood circle a bit.
Eat well. Your body mostly generates heat by moving muscles, but also by digesting. If you eat well you will be warm — toasty in your sleeping bag after a rich tasty dinner. Conversely, being hungry will chill you.
Eat warm. Besides enough food, warm food and liquids also helps getting your body warm. Your body mass compared to food mass is quite large and you can only take in food in moderate temperatures (saliva stops working at above 40 degrees), so energy transfers are not large. The true function of eating warm is actually in effective digestion, your body needs to warm the food up to that 36.5 degrees if you don’t. And that costs energy and time.

Outdoor Multi day Sleep System

Many refer to the gear used to sleep outdoors as a “sleep system”. It is often composed of the few fundamentals: sleeping pad, sleeping bag and tent. Some prefer a hammock or just a tarp instead of tent, but a pad and bag are a must in any case. Sorted by importance from most to least important sleeping system gear parts:

Sleeping Pad

Purpose: Sleeping pad provides insulation from the ground. Depending on R-factor (conductivity) there is a great variety of how effectively pads prevent heat loss.

Types:

Inflatable: are light and packable, warm, can be thick and comfy, but expensive, can burst, need to be inflated and deflated every day. There are some new clever ideas on inflating them on the market, check out ThermaRest Speedvalve. Or just DIY your own inflating “machine” — this proved to be essential tool when inflating 2 matresses every day for 8 nights.
Self-inflatable: big and comfortably self-inflatable, can be thick but then heavy and bulky, can burst, deflating them is a pain. Mostly not suitable for multi-day hikes.
Cell-foam: cheap, clunky, indestructible, not as warm as inflatables.

We have used a combination of ThermaRest inflatable and a cell-foam “armaflex” roll mat which we have used for other daily camping purposes:

seating while cooking and eating outside,
additional protection for below the tent
spare in case of burst of our ThermaRests
as a clean surface to put items on while packing/unpacking
because of this we were also each 300g heavier and bulky giant pads were very annoying sometimes when moving through bushes and disabled us to put on rain covers

Inflatable pad features to look for:

Is sturdy — you don’t want a puncture on day 2
Has sufficient R coefficient — depending on your needs
Easy to inflate and deflate (!)
Is not super loud when you move on it
Doesn’t have plasticky, sticky feeling if any of your skin touches it
Is light (our ThermaRest NeoAirs are about 600g)

Sleeping bag

Purpose: Provides insulation against convection and reflects heat. Sleeping bags are crucial in providing you with warm sleep, which enables you rest and not lose energy to heat.

Warmest, lightest and smallest sleeping bags are down sleeping bags. They are off course also the most expensive, really hard to wash and completely useless if properly wet, after which they are also very hard to dry.
Sleeping bags get large and heavy … and expensive. If your bag starts weighing above 1.5 kg you should starting saving for a lighter one. Expect to spend about 200–300€ for an affordable down sleeping bag which will get you through everything down to 0 degrees with a good pad.
Pad first: I would choose cheap sleeping bag over a cheap sleeping pad anytime. It is much more important and hard to prevent heat loss from conduction (touching ground) than to convection (moving air).
Sleeping in clothes increases warmth, esp. if you stuff a down jacket inside the bag, on top of you. There was this misconception going around that you should sleep in less clothes in the sleeping bag, which is nonsense. Clothes will always increase your warmth; they will also constrict your movement, be uncomfortable when sleeping, bring in dirt to sleeping bag.
To increase warmth of a sleeping bag, do not put heavy blankets over, as this will squeeze air of of it and reduce its insulation. Put the blankets inside — if there is space — or just dress more. You can also put an aluminium warm water bottle between your legs or under your arm.

Tent

Purpose: Provides protection against getting rain and dew (phase change heat loss), wind chill (convection heat loss), insects and animal invaders. However, temperature differences between outside vs inside tent are not large, most often a few degrees (normal hiking conditions). Compared to tens of difference of degrees between your sleeping bag inside vs outside temp, tent is not considered an insulation gear. You can’t sleep in the tent without a sleeping pad (conductivity), but mostly you can sleep fine with just a pad and a sleeping bag in dry weather.

Tent is most likely the single heaviest item on your gear list and it can get very large.
It can also get very expensive. Hilleberg tents can cost 800€. Very good tents for 2 can cost 500€, but those OK are 200€.
Like with the GoreTex jackets, tents seem to get disproportionally a lot of attention and are expensive in regards to their importance in both managing heat loss and comfort. Invest into sleeping pad first, then sleeping bag, lastly tent.
Probably most reasonably well produced tents will hold a prolonged rain just fine. They might fail in heavy winds, however. Achieving stability, air circulation, water-proofness, protection against bugs at the same time as low weight is hard and it costs.
Besides heavy rain, the source of wetness inside the tent can be condensation on tent walls. Two-wall tents work much better and well constructed tents have better engineered air flow circulations and water droplets not falling on your bag … and face.
Set your tent up thoroughly to achieve good air circulation. You need enough fresh air not just to breathe, but to dry your wet stuff inside the tent. Tents that are well designed and well set-up will provide this.
Make sure you use all and many guy lines to secure your tent if there is a storm coming. It is way to easy to skimp on this, but we learned it the hard way: we got our tent poles bent twice on an expensive tent. They didn’t break and tear the fabric — which would be a disaster — but deformed our tent which then lost insulation and water-proofness.
№1 way to destroy your tent is when people stumble over your guylines. Mark them. Walking sticks work well for this.
You will mostly want to place your tent on soft grounds, grass preferably, therefore light, small, square aluminium stakes will be best. You should be able to push them in by hand. If you can’t then rather search for heavy logs and stones as stakes which aren’t stuck properly will be pulled out easily by the wind.
Get to know your tent well and how to set it up properly. You can destroy your tent by this and sometimes things are not as self evident as they should, so read manual, use YouTube or ask. This is important as you will need to set up tent in dark, in rain, in cold and hungry.
Train your tent set up before you go to a hike. Get into routine and study it.
Difference in weight between 2 and 3 person tent might be small, but can provide very welcome space when out for the 7th day or one whole day waiting for the rain to end.
Tent is not just for sleeping but for storing your gear overnight. Large vestibules are good, but maybe having your stuff inside is more reachable to you and less to foxes and snakessss.
You will want to hang your wet clothes somewhere. Due to morning due it makes sense to hang them inside the tent, but usually they are not really prepped for that, so experiment.

Sleeping clothes

Do not sleep naked and make sure you do not sweat! Your body oils will not just make your sleeping bag stinky and dirty, but will also contaminate down feathers. If you are too warm, rather sleep in more clothes and just partially cover yourself with bag.
Sleep in dry non-compressing base layers and put on thick loose woolen socks.

Sleeping pillow

For many pillow is a must, but can be made out of a clothes bag and stuff put in it. However, if you will be doing this days after days it might be wise to invest into a sub-hundred grams pillow which will make you sleep much better and reduce your prep time a lot.

More gear guides:

Multi-day hiking Clothing
Multi-day hiking Boots & Socks