Many people think of just the sleeping bag when they are contemplating the comfort of a good nights sleep. However its your entire sleeping system that includes your sleeping bag, liner and your sleeping mattress and its combined warmth will have a significant impact on how comfortable your sleep is.

In this article we hope to give you some knowledge and tips to help you with your decision making for your sleeping system investment.

Sleeping Bags

Your sleeping bag will quite possibly be one of your most expensive outdoor equipment investments you will make & its key to make sure your getting the most appropriate sleeping bags for your needs. Here are a few key things to keep in mind when looking for your new sleeping bag.


Image: Lachlan Gardiner

Temperature Ratings

Lets start at the beginning and as you most likely know both men and women sleep at different temperatures with men sleeping generally a few degrees warmer than a women does. Women’s extremities also tend to feel the cold as the nerves that control blood flow to the hands and feet are more sensitive in women than in men, so when the temperature drops, their vessels constrict more, warming blood flow slows, and their extremities feel cold. With this in mind it is recommended that a women purchase a sleeping bag that is warmer than a man would get for the same environment.

To gauge which sleeping bag is the most appropriate for a particular environment many sleeping bags such as the Western Mountaineering, Mont & Sea To Summit range have had their temperature rated using European EN13537 standard. This standard gives you a good idea on how warm or comfortable a particular sleeping bag will keep you and a guide to compare different sleeping bags. For a sleeping bag to be given the EN13537 it requires a thermal manikin test which produces four temperature results — upper limit, comfort, lower limit and extreme. These temperatures were worked for normal sleepers.

The standard measures four temperature ratings:

  • Upper Limit — the temperature at which a standard man can sleep without excessive perspiration. It is established with the hood and zippers open and with the arms outside of the bag.
  • Comfort — the temperature at which a standard woman can expect to sleep comfortably in a relaxed position.
  • Lower Limit — the temperature at which a standard man can sleep for eight hours in a curled position without waking.
  • Extreme — the minimum temperature at which a standard woman can remain for six hours without risk of death from hypothermia (though frostbite is still possible).

For the purpose of these measurements, a “standard man” is assumed to be 25 years old, with a height of 1.73 m and a weight of 73 kg; a “standard woman” is assumed to be 25 years old, with a height of 1.60 m and a weight of 60 kg.

EN temp ratings

Examples of the EN13537 Temperature ratings on the Sea To Summit Latitude sleeping bag

Most sleeping bag manufactures who use the EN13537 standard will show the “Comfort” which as discussed is the best gauge for a women, the “Lower Limit” is a great guide to the limit a sleeping bag will keep a male warm while the “Extreme” rating is a temperature that you and your sleeping bag are unlikely to get too but good to know just  in case. However be weary as some retailers will advertise the “Extreme” rating so be sure to confirm what the temperature rating is, then choose the most appropriate bag for you.

A number of American sleeping bag manufactures haven’t crossed over to the EN13537, much like the way America continues to use the imperial system for measurements. If comparing manufactures such as Nemo who are yet to use the EN13537 its best practice to take their temperature rating as a close equivalent to the “Lower Limit” rating.

Naturally all of these temperature ratings are assuming you are also wearing the appropriate clothing such as thermals and a sleeping mattress for the environment that you are sleeping in.

Sleeping Bag Shapes

Sleeping bags shapes are designed to achieve a balance between comfort and performance while taking into account the priorities of the sleeping bag user. The larger a sleeping bag is internally, the more room there is to move however the more air there is for the body to heat. Thus an increase of space in a bag will allow for more room to move around, however it will reduce the bag’s thermal efficiency.

Sleeping bags traditionally come in three shapes:

  • Mummy — This is the most thermally-efficient sleeping bag shape. This design is wide at the shoulders with a pronounced taper to a narrow foot, reducing the amount of space – and air to be heated – within the bag. These bags offer the best warmth for minimum weight ratio. Mummy bags are perfect for the adventurer looking for a compact, light weight, technical bag. The downside to a mummy shaped bag is its narrower fit that reduces the room to move within the bag, which some people may find restrictive. Its best to lay on one before you buy, particularly if you’re claustrophobic or like to roll around in your sleep.
  • Tapered rectangular bags — These sleeping bags are a little roomier than a mummy bag, they taper at the foot, which helps in reducing dead space and the air to be heated within the bag. These sleeping bags are a good all rounder as they are comfortably roomy, while still being efficient enough to pack down to a good size and still give a good warmth to weight ratio.
  • Rectangular bagsThese sleeping bags are wide at the feet as thy are at the shoulders, thus comfortable for someone who like to move around when sleeping or is a little larger. Rectangular bags are great for use when warmth, packed size and weight are not critical as they are generally larger, heavier and less technical bags.

    Caroline Gleich/Patagonia

    Caroline Gleich/Patagonia

Down & Loft

Down is the natural plumage found at the undercoating of geese and ducks. When clustered together, high-lofting down plumules (tufts) trap air with unparalleled efficiency. Down is an exceptional insulator, revered for being light, highly compressible and breathable. Down is relatively durable as well, if cared for properly, down plumules retain their near-original lofting ability for decades.

Loft measures how many cubic inches 1 oz. of down can fill inside a tube after being aerated and has had time to resettle. Downs loft generally ranges from 450 to 900. In outdoor equipment, fill ratings commonly fall between 600 and 800. The higher the loft the greater quality and results in a lighter product, with premium down coming from very mature geese and is graded 750 to 800+ (hence its greater expense). Simply put the higher the Loft the greater the warmth to weight ration will be.

Traditionally a downfall of down is when it gets wet. Down tends to collapse, clump and can no longer insulate. In addition, down is very slow to dry, often requiring a day or more. This is down’s biggest issue however most down sleeping bags will use water resistant fabrics to help counter act this problem. Recently, several water-repellent treatments for down have been introduced. They involve a durable water repellent being applied to down plumules at a molecular level (kind of like the Teflon coat on a frying pan). Treated down can retain its loft if exposed light moisture. However it will still clump if the sleeping bags is saturated. Treated down will also dry a little quicker than untreated down.

Sleeping Bag Liners

A sleeping bag liner is a very wise investment for a number of reasons. Firstly is the way they will keep your sleeping bag clean from dirt & grime off your body when on multi day hikes. Cleaning a sleeping bag is a chore which you don’t want to be doing after every bushwalk however throwing you liner into the wash with the rest of your camping clothes is no hassle at all.


Secondly a liner can provide some warmth to your sleeping bag system. For example a light weight Sea To Summit cotton/silk or 100% silk liner is great for summer where the temperatures are warm and that is all you need to be comfortable for most of the night, with your sleeping bag opened up & ready to be pulled over you when it gets chilly early in the morning. Another great way to add some warmth to a sleeping bag and make a bag that is only a few degrees below 0 degrees warm enough for winter camping is to use a Sea To Summit Reactor which is made using a Thermolite®fabric. This liner can boost the temperature of a bag by a number of degrees without a huge weight penalty or the expense of needing to purchase a new sleeping bag for the odd snow camping trip.

Sleeping Mattress

Your sleeping mattress is a key part of the sleeping system as this is what keeps you off the ground and insulated. Traditionally many hikers used a closed cell foam roll mat or a inflatable lilo style mat which where bulky, could be heavy in the case of a lilo and not overly warm but hey it was more comfortable than sleeping on the ground which is what hikers from the era of Paddy Pallin & our grandparents did.

In 1971 Therm-a-Rest revolutionised the way we enjoyed the outdoors when they invented their self inflating mattress that packed down to a relatively small and light size but still gave the sleeper a warm insulated sleep.


The original press used to make the first prototype mattresses and the original Therm-a-rest production mattresses from 1972.

More recently the insulated air mattress has become extremely popular with a number of brands such as Seat To Summit, Nemo and Therm-a-rest producing mats that are very compact, light and still give excellent warmth due to special fills and linings to the mattress.

Many sleeping mattress use the R-Value which is a measure of thermal resistance; the higher the R-Value, the more thermally –resistant or, better an insulator, a given mat is. A good gauge is a mat with a R-Value below 2 would be good for Summer, between 2 to 4 would be appropriate for most conditions that would be faced in Spring and Autumn and if you are interested in sleeping mat for early Spring, late Autumn or Winter conditions a R-Value of over 4 is advised. Many people will use two mattresses, a closed cell foam mattress and an insulated inflatable one with a combined R-Value of at least 5 for snow camping in winter. Again these R-Values & recommendations are still just a good gauge with the warmth of your sleeping bag and how warm you sleep to be factored in when deciding which mattress is best for you.

Sleeping System Tips

Image: Jack Williams

Image: Jack Williams

It takes most experienced hikers years of pushing the limits of their sleep systems to work out how to get the most efficient and comfortable sleep in the outdoors with many people developing an unique system over time.

However, if you’re new and don’t have the time to gain a few decades of experience, here are some top tips on adapting your sleep system to achieve warmth across a range of temperature.

System — Your sleep system includes your sleeping bag, liner and your camp mattress. The warmth of your mattress will have a significant impact on how warm you sleep. Using the same sleeping bag and sleeping on a Sea To Summit Comfort Plus Insulated mattress will be a very different experience than sleeping on a closed cell foam pad. A Sea To Summit Reactor sleeping bag liner can also be great cost effective method to boost a sleeping bag for those odd cold winter trips.

Clothing — Were not talking about a Victoria’s Secret nightie here but sleeping in a fresh set of Merino or synthetic thermals will help you stay toasty, as a bonus they will also keep your sleeping bag clean from body oils and grime from the days activity. I keep a spare set for sleeping in only and keep them stored in a dry bag for peace of mind. However don’t get tricked into putting on to many layers, as your body will struggle to warm them and your sleeping bag up. Head to our Tips on How to Sleep Warm article for more ideas.

Temperature Range — Take advantage of the EN & temperature ratings as they are a great guide in helping you find a sleeping bag that will meet your needs. While it’s obviously important to get a bag with ample warmth, it’s also important not to get a bag that’s too warm. However, also keep in mind the versatility a zip to the sleeping bag can add, the way it can let air vent out through the lower legs and feet and the extra warmth provided by a liner.

Fit — It’s important to be able to not feel to constricted in your sleeping bag, however you don’t want so much room that you spend all your energy heating empty space. If your on the larger size make sure the sleeping bag isn’t too small, as you will compress the insulation and create cold spots. Find a bag that fits your width as well as your length.

About The Author

Dave Casey

Dave has worked as an International Expedition Leader and in Outdoor Education for over 15 years. He has extensive travel and guiding experience in Australia, NZ, Asia, South/North America and Europe. In his spare time Dave is a keen bushwalker, mountain biker and climber while also dabbling in some mountaineering and sea kayaking.

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