Tips to Maximise the Effectiveness of Your Sleeping Kit

posted in: Tips & Tricks | 49
Tarp and bivvy in spring sunlight
Look after your sleeping kit and it will look after you. Photo: Paul Kirtley.

Whether you are in a static camp or making a journey, looking after your sleeping kit is a priority.

Moisture retained in your sleeping bag will significantly reduce its thermal efficiency. A damp bivvy bag will increase heat loss by evaporation.

Moisture From Within

We all give off moisture while we sleep. If we are too warm we sweat. This is obvious and can largely be prevented by removing layers of clothing, unzipping sleeping bags, opening bivvy bags and generally increasing ventilation.

Even if we are not sweating, however, we are giving off moisture all the time. Imperceptible perspiration helps keep our skin from becoming too dry. It also means that, during sleep, we can lose around a third of a litre of moisture into our sleeping bag without even realising.

Moisture From Without

Air at night is typically cooler than during the day. Cooler air has a lower capacity to retain moisture, which translates to cool, damp air and the formation of dew.


Bivvy bag and sleeping bag covered in frost and light snow.
With the right knowledge, bivvying in the Arctic is possible but it brings with it some specific challenges. Photo: Paul Kirtley.

Dew is a form of condensation and it tends to increase as the air temperature drops.

Condensation of moisture from inside your sleeping equipment also tends to increase as the temperature drops. The main reasons for this are that, first, the cooler air outside is more likely to be saturated and therefore evaporation of the moisture from your perspiration is harder to achieve; second, as the external temperature of your sleeping equipment decreases, water vapour is more likely to condense on the inner surfaces.

In extremely low temperatures (around minus 20 Celsius and below), condensation can actually just freeze on the inside.

Ground Moisture

The ground is often damp. Laying on the ground will make whatever is between you and the ground damp too. Lying on frozen ground or snow also has the potential to introduce moisture to your sleeping equipment.


An obvious potential source of moisture on the outside of your sleep system is rain. Even if the outer cover of your sleeping kit is waterproof, it just being wet will increase evaporative heat loss. This may be unavoidable while it is raining but make sure you get it dried off as soon as you can.


As air temperatures drop below freezing in the winter months, or at higher altitudes, frost can form overnight (where condensation would form at higher temperatures). Again this can be from moisture in the air (forming on the outside) or perspiration forming on the inside of sleeping equipment.

Don’t Breathe

Frosted sleeping bag in arctic forest
A sleeping bag hanging up to air off in the arctic forest. Note the frosting from my breath on the outside of the bag. Photo: Paul Kirtley.

All the moisture we have discussed so far has either been due to perspiration or the environmental conditions. Your breath contains a lot of moisture (you can see this on a cold day). If you breathe into your sleeping bag at night, then you add much more moisture to it than you do if you breathe outside of it.

On chilly evenings this extra moisture may cause you to be cold during the night. It can also be difficult to get rid of unless you have the right conditions the next day.

In consistently sub-zero (Celsius) temperatures, breathing into your sleeping bag can cause serious problems, with the build up of frost within your sleeping bag impossible to remove unless you enter a warm, dry environment such as a cabin or heated tent. Breathing moisture into your sleeping bag in an Arctic environment will literally render your sleeping bag unusable in a relatively short period of time.

Get Some Air

Under most conditions, the primary way you should remove moisture from your sleeping equipment is to air it out.

Get your sleeping bag airing as soon as you get up. The bag will still be warm and this warmth can mobilise moisture to evaporate.

Open your bag out to maximise the effect.

Sleeping bag opened out on top of a tarp
Open out your sleeping bag to air off. Photo: Paul Kirtley.

Get Some Sun

A light breeze of relatively dry air will do a good job of removing moisture from your sleeping kit. If you can get the sun on your sleeping equipment – particularly your sleeping bag – all the better.

Sleeping bag draped over a tarp in the sun
If you can, get some sun to your sleeping bag. Photo: Paul Kirtley.

Air All of Your Kit

While your sleeping bag is most affected by moisture, all your other sleeping kit contributes to keeping warm and should be kept as dry as possible.

Sleeping bags, mats and bivvy bags on top of tarps in the Spring sunshine
Air all of your kit if you can – here taking advantage of early Spring sunshine. Photo: Paul Kirtley.

What If It’s Raining?

If it is raining or your are concerned about the possibility of rain, then you can hang your sleeping bag under a tarp using a hanging line.

RAB Sleeping bag on hanging line under a tarp
If you have a hanging line under your tarp, you can air your sleeping bag on it. Photo: Paul Kirtley.

If conditions are particularly humid then there may be no immediate benefit to airing your sleeping bag at all. In this case, leave it in your bivvy bag, or tent, until the opportunity to air it arises.

Some Extra Considerations For Your Sleeping Kit

If you have placed all your sleeping kit inside a bivvy bag, then the bivvy bag will have been in contact with the ground. This can leave the bag really quite damp and it may need airing/drying for longer than either your sleeping bag or sleeping mat.

Bivvy bag drying over a tarp.
Your bivvy bag may need to be dried out more/for longer than other sleeping kit. Photo: Paul Kirtley.

Condensation can form on the underside of your sleeping mat too, so make sure you air this off so it is packed away dry, ready for the next evening.

In sub-zero temperatures, water vapour may well have frozen on the interior of your bivvy bag. Below around minus 20 degrees Celsius, this happens even with ‘breathable’ bivvy bags. Simply turn the bag inside-out and shake off the frost.

A Little Effort Pays Dividends

Paying attention to the care of your sleeping kit will maximise its effectiveness in its intended purpose, i.e. keeping you warm for a comfortable night’s sleep. Tiredness, irritability and easy fatigue are all effects of poor sleep. Taking a few minutes in the morning to take advantage of any sun or breeze to air out your sleeping kit will always pay dividends.

On a wilderness trip or expedition good rest is much more important than on a leisurely camping weekend. But you’ll also be more likely to need to pack up and move on each day in order to reach your destination. Even 15 minutes of airing while you make a brew and eat your breakfast can make a significant difference to the condition of your sleeping kit.

Sleeping bags and liner in the sun
Sleeping kit getting morning sun and air on a canoe trip on the French River, Ontario. Photo: Paul Kirtley.

What Do You Do?

What other tips do you have for keeping your sleeping kit in top condition? Let us know in the comments below…


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Paul Kirtley is owner and Chief Instructor of Frontier Bushcraft. He has had a lifelong passion for the great outdoors and gains great satisfaction from helping others enjoy it too. Paul writes the UK's leading bushcraft blog as well as for various publications including Bushcraft & Survival Skills Magazine.

49 Responses

  1. John Clarke

    Another great article !
    I learn something new and valuable every time.

    Keep up the good work


  2. Duane Yates

    Hi Paul
    Good article as usual, plenty more useful information 🙂
    With regard to condensation inside a bivvy bag, I usually keep my clothes for the following day inside my bivvy bag, is this a good idea or not?
    Cheers Paul,
    Take Care

    • Paul Kirtley

      Hi Duane,

      Thanks for your comment – pleased you liked the article.

      Keeping clothes inside your bivvy bag could potentially add some moisture to them but it does have the advantage of keeping them warm.

      I think keeping clothing inside depends on what the priorities are. For example, in arctic conditions, I place my boots inside the sleeping bag stuffsac (turned inside out) then place this between the sleeping bag and bivvy bag down near my feet. It prevents them from freezing solid overnight…



  3. David Willis

    Another great article Paul, no excuses for folks not to be getting a good nights sleep if they follow your advice.

    To ensure I sleep well, I change out of my day clothes, which are usually damp, into another set (dry ones) appropriate to the conditions. That way I’m not introducing more dampness into my sleeping bag!

    In the summer months, I sometimes use a cotton liner, and just fold the sleeping bag over when it gets cooler – and of course they are easy / quick to wash ensuring your bag stays clean and hence works far better.


    • Paul Kirtley

      Hi David,

      Thanks for your comment. Liners are indeed a good idea. They definitely extend the thermall efficiency and life of your sleeping bag. Also if you use a down bag a liner reduces the cleaning bills considerably!

      Thanks and all the best,


  4. skipjames

    Good article. I,ve been considered mad in scout camp as I always getting the lads airing the bedding even in summer camps. Sadly most do n’t . But it does mean the air smells sweet when you wake them up. people are always amazed that their kit is so damp caused because they don’t air their bedding and kit.


    • Paul Kirtley

      Hi Gwyn,

      Good to hear that you are trying to instil some self-discipline into the lads. They’ll thank you for it in the long run 🙂

      All the best,


  5. Jason

    Thanks for another great article Paul. I try to air my sleep kit first thing after I wake. Although I must admit that coffee sometimes bumps it to #2.

  6. joseph harvey

    i read that the men on many polar expeditions sweated while working and once they finished the sweat would then freeze and they would turn their tops inside out and shake the ice out this reportedly worked very well, but then they were tougher in them thar days 🙂

    • Paul Kirtley

      Hi Joe,

      Shaking frozen perspiration out of the inside of garments or sleeping kit works well with shell layers (such as bivvy bags in the case of sleeping kit) but not with some insulative materials, where the moisture becomes frozen within the garment/sleeping bag.

      And yes, they probably were tougher… 🙂

      All the best,


  7. Bart Leenders

    Hi Paul,

    great notes from the woods. Your tips are a puller to your courses I notice.

    I’ve been told that the ultraviolet rays from the sun kills bacteria and kills the sweaty smell of your sleeping bag. It seems to work for me or maybe it is the airing in total.

    And a quick wash of the larger body parts just before bed time, helps keeping moist out. Plus it’s less sticky.

    Cheers, Bart

    • Paul Kirtley

      Hi Bart,

      Thanks for your comment and your extra tips.

      It seems hanging things out to dry works in other areas too:

      On a recent trip in Canada one of the group, who works in the medical profession, was hanging his plate, mug and cutlery up in the sun/breeze. His comment was that “the best way to kill bugs is to dry them out”.



  8. david

    hi paul
    my sleep system consists of a bivvy bag.sleeping bag inside and a liner.
    i always air my kit one way or another. but i always strip the system down into its constiuante parts clean and dry them. but i always use a insect spray to make sure i have no little terrors in there.
    dave d

    • Paul Kirtley

      Hi David,

      It’s good to hear from you again.

      It sounds like you have a very good personal routine with maintaining your sleep system in the field. Nice to see you are so organised and disciplined about it. These things make a difference.

      All the best,


  9. Richard

    Hi Paul,
    thanks for Another great article. With regards to your article do you place your sleeping bag and roll mat/thermarest inside the bivi bag or do you sleep inside the bivi bag with the mat on the ground.

    Thanks Richard

    • Paul Kirtley

      Hi Richard,

      Thanks for your comment – I’m glad you enjoyed the article.

      In answer to your question, I put the sleeping mat and sleeping bag both inside the bivvy bag. I’ve found with modern inflatable mattresses of the Thermarest type that you just slide off if the mat is on the outside. Keeping everything contained in the bivvy bag keeps you on the mat as well as keeping everything warm and dry.

      All the best,


      • Richard

        thanks for the response Paul, i was a little concerned about puncturing my mat do you have a ground sheet under the bivi?

        thanks again

        • Paul Kirtley

          Hi Richard,

          No, I don’t use a groundsheet. I try to keep kit to a minimum. Just try to avoid camping under hawthorn and do a visual sweep for the likes of brambles and sweet chestnut casings.

          All the best,


          PS I’ve been using the same thermarest for nearly 10 years and it’s fine.

          • Richard

            Thanks Paul, im going to give it a try over the bank holiday weekend.


  10. Lou

    Great article..….again. All of it was really useful and relevant – thank you. Just to reinforce what you say I’d like to share some of my experience from three winters in Norway in the mid 80s. Then, the first versions of waterproof vapour permeable L-zipped bivvy bags were available, as were synthetic sleeping bags rated to about -20C. The latter were heavy and typically occupied 40 litres so could be a snug fit in the bivvy bag! The mostly dry overnight temperatures hovered between +2C to -25C.

    Given these things, it was still possible to sleep very comfortably (warm and dry) with a good closed cell mat underneath and to keep internal condensation to a minimum by leaving a slim 4-6 inch opening at the top of the bivvy bag (although you have to be sensible in falling snow and wild wind). This didn’t stop a crust of ice forming on the outside after a couple of hours and that affected breathability. However, giving the bag sharp bangs from the inside at every opportunity easily dislodged this crust and helped to maintain a reasonable microclimate.
    The top tips we gleaned from a sustained period in such conditions were:

    • Damp kit – we dried damp kit off by placing it next to skin whilst sleeping (it’s only uncomfortable momentarily and drying conditions might be poor the next day),
    • Wet boots – we brought boots inside the bivvy bag after having taken all loose snow off (so avoiding frozen boots and also enabling you to wear them if you’re caught short in the night). If you place them at the head end it’ll help to introduce a condensation-reducing gap between you and the inside surface of the bivvy bag,
    • Hot water – we filled flasks with boiling water last thing and brought them inside the sleeping bag (it’ll still be hot enough for porridge and a brew first thing in the morning),
    • Loft – the point about airing sleeping bags regularly is really important because its restorative effects on loft can make a noticeable couple of degrees of difference to warmth – at these temperatures that’s worth having, and
    • Be aware – we kept from snow-laden boulders and other structures which take every opportunity to shed a few pounds of snow if you sleep too close!

    In the end it’s mostly all down to common sense. Of course, nowadays the improvements in knowledge and kit help to make this a little easier (and lighter) so there’s less excuse not to get out and stay out in the snow.


    • Paul Kirtley

      Hi Lou,

      I’m glad you liked the article and thanks for taking the time to share your experience too.

      I hope your comments will further encourage people to get outdoors and manage their sleeping kit better in all conditions.

      Warm regards,


  11. Jake Pyett

    Hi Paul,

    I just wanted to know what your opinion is on sleeping in a wool blanket instead of a sleeping bag?
    I’ve been interested in sleeping in a blanket outdoors, just to make change from using a sleeping bag.

    Does a wool blanket have any pros or cons, and does the build up of moisture effect it in different ways than it does with a sleeping bag?

    • Paul Kirtley

      Hi Jake,

      Wool blankets can be very warm and comfortable. There are blankets of varying quality out there though, so choose the best quality you can get. Hudson’s Bay point blankets are lovely but very expensive (more expensive than many sleeping bags). You can get some good ex-military wool blankets which are very reasonably priced and quite thick. When using a wool blanket you need to make sure you tuck yourself in properly as it is not quite as easy for the novice to ‘seal’ the blanket up as it is with a sleeping bag. Wool blankets can also be quite heavy compared to a modern down sleeping bag. There doesn’t seem to be much of an issue with moisture, as long as you air the blanket out.

      I hope this helps.


  12. Jake Pyett

    Thanks Paul, that’s a big help.

    I just checked out a few video tutorials online that show some pretty good ways to tuck yourself in. Looks quite warm when its done properly. There’s only one way to find out how well it works though!

    Thanks again,

  13. nigel brandon

    hi paul
    great article will be putting the tips to good use at scout bivouac camp we usually put sleeping bags into orange plastic survival bags which do keep the scouts nice and warm and they do air them in the morning will make use of the tips

  14. Juul Platenburg

    Hi Paul,

    Having just recently discovered your site (definitely a newby on the bushcraft front), I must say that I’m impressed with the clear presentation of nearly all subjects. The pictures and clips used further clarify already clear words.

    One thing that I missed in this article on maximizing the effectiveness of your sleeping kit is proper storing when you’re back home. Your thermarest/sleeping mat should be taken out of the stuff sack and unfolded/laid out with the valve opened. The same goes for your sleeping bag of course.

    Thanks and keep up the good work!


  15. Stephen Walker

    Hi Paul

    There’s always some / many gems in these articles that I didn’t know before.
    Knowledge is power!

    I have finally decided on a new tarp so this info will be useful if I manage to get out in the snow when it arrives.



    • Paul Kirtley

      Hi Steve,

      Yes, I do try to get some random thoughts down in my notebook from time-to-time. 🙂

      I then distil them down into articles.

      I’m happy you are finding this stuff useful.

      Knowledge is indeed power!

      I hope you enjoy your new tarp. Which one did you go for in the end?



  16. barry Mcindoe

    Hi Paul, many thanks for sharing your invaluable information. It was both pleasurable and informative and i look forward to reading more. Planning a trip to Hoy next month with the bivvy bag and tarp, its been a number of years since i last experienced a winters trip, but im thoroughly looking forward to it.



    • Paul Kirtley

      Hi Barry,

      Thanks for your comment. Your feedback is much appreciated.

      Your bivvy exped to Hoy sounds exciting. Let us know how you get on.

      Warm regards,


  17. Randell

    Excellent post, I had no idea that breathing into your sleeping bag was a bad idea, i do it all the time, always made me feel warmer. Tho im my defence i live in Australia so the next day is normally pretty hot so i never notice any lasting effects of moisture 🙂 This is great advice tho and i’ll have to be mindful next time i go camping not to do it. cheers for the advice.

    • Paul Kirtley

      Hi Randell,

      Well it depends on how cold it is and how easy it is to air out your bag. As you say, in warmer climates it’s not so critical as you can dry out the bag during the day. But breathing into your bag can still make you chilly if it gets cold overnight.

      Glad you found it useful and thanks for your comment.

      Warm regards,


  18. Rody Klop

    Well written artice Paul.

    This goes for the clothes, socks and shoes as well. Shoes on a stick turned around. Give those feet a good rest. A hanging line under the tarp is what I always use, also easy the finding back your headlight etc. So even when raining I can still hang clothes, socks and sleepingbag under the tarp.

  19. Bill Jackson

    On a forestry contract in the extremely rainy Queen Charlotte Islands, I would put a metal pail full of hot rocks in my tent at night, sitting on a spare shirt to protect the tent floor. When you’re tenting for a week or more in rainy conditions, moisture accumulates regardless of how careful you are. Dry heat helps to move the moisture out of the tent.
    Do not use a propane (or any) stove for this purpose. Water is one of the main products of combustion. A couple of big rocks work, just make sure they’re not directly on the floor of the tent and are not hot enough to damage the tent material.

  20. Bill Jackson

    I might add that it would be even better to use the rocks in the morning, when you’re out of the tent. I didn’t have that option because it takes time, and I was working.

  21. Shaun

    Hi Paul. I’ve been watching and reading your posts for quite some time now. I only started a couple of months ago with hiking and even tried my hands on a bit of bushcraft/survival in building shelters and starting fires without using lighters or matches. Let’s just say, the making of fire is doing much better than the building of shelters, lol. I also went out and bought, well, in terms of my wallet, expensive gear for this hiking session, could almost misjudge me as Special Forces with the whole kit, but then, only after a couple of your posts, I saw I’ve spent thousands of Rands on non essential kit/items. And now again, with this post, I learn things that I didn’t think was so important. Thanks Paul, for your teachings over Twitter, it surely helps me here in South Africa!!

  22. Nick Ford

    Massively useful article, full of not-so-common sense – especially links to rigging a hanging line under the tarp to air kit when there is risk of rain.

    Thanks again!

  23. Dave H

    Thanks for more little nuggets of knowledge Paul. I look forward to these posts, and appreciate the time and effort involved.
    All the best, Dave.

  24. Neeman

    Great information

    I camp under a tarp without a bivi sack, and stay vey dry
    Could you help with this question
    What is the advantage of a bivi sack in keeping dry from external moisture
    What is the disadvantage of the inner condensation from the bivi bag


  25. Andrew walker

    Hi Paul

    Thanks for taking the time and sharing you experiences and knowledge with us all .
    i followed the link from the subscription email service it is very helpful in allowing the taking in of information in small doses aswell as saving the link in my inbox for revisiting later .
    I noticed in the comments a question on external moisture and pros and cons to bivvy bags and was also wondering.
    I have twice woken mid morning while tarp and hammock camping next to water with the morning mist all around with the outer shell of my sleeping bag quite damp . The question is do you think the angle at which you pitch a tarp has any influence on mist and fog build up under it and would a sharper angle help in condensation run off on the under side of tarp or hinder it due to minimal air flow .

    Regards Andy

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