A comfortable sleep is always important, but it’s even more important when you’re out adventuring. That’s why choosing the correct sleeping equipment for the terrain and temperature you will be sleeping in and your own preference is so important. Sleeping bags, inflatable mats, pillows and liners are all valuable parts of a sleep system that can make the difference between a good or bad night in your tent. R-numbers, insulation fill, inflation method and time of the year the item is intended for, all play a role in choosing the right gear for you.
How do sleeping bags lose heat?
If you paid attention in your Physics class you’ll already know that the three primary mechanisms of heat loss are conduction, convection, and radiation. The goal of a good sleeping bag and mat is to stop these mechanisms in their tracks to prevent heat loss.
• Conduction is the transfer of heat from one object to another through direct contact. For example, if you touch a hot surface, heat is transferred from the surface to your hand through conduction. In a sleeping bag, conduction occurs when heat is transferred between your body and the ground, or between different parts of your body that are in contact with the sleeping bag. A good sleeping system (bag and mat combination) will have suitable insulation to minimize heat loss from conduction by providing a barrier between your body and cold surfaces.
• Convection is the transfer of heat through the movement of a gas or liquid. For example, heat can be transferred from a hot cup of coffee to the air around it through convection currents. Convection in a sleeping bag occurs when heat is transferred away from your body by the cold temperature of the air, either within the sleeping bag or in the air around it. A good sleeping bag will be designed to minimize convection by reducing the amount of air that can circulate within the bag, and by providing insulation that traps warm air close to your body.
• Radiation is the transfer of heat through electromagnetic waves. For example, the sun transfers heat to the Earth through radiation. To put it simply, direct contact is not needed for the transfer or loss of warmth. Radiation in a sleeping bag occurs when heat is transferred between your body and the surrounding environment through electromagnetic waves. A good sleeping bag will have insulation that helps to minimize heat loss due to radiation by reflecting your body heat back toward you, rather than allowing it to escape into the tent. Some outdoor sleeping mats incorporate reflective foil surfaces to prevent heat loss through radiation.
How does sleeping bag insulation work?
Insulation is the key component for keeping you warm. Down and synthetic are the two main insulation types used in sleeping bags and mats. In simple terms, insulation works by trapping air, creating a barrier to heat loss from convection and conduction.
Which insulation is best for sleeping bags, synthetic or down?
Down insulation is made from the soft plumage found underneath the feathers of waterfowl, such as ducks and geese. The insulation works by trapping a layer of air between the down clusters, which creates an insulating barrier of air that helps retain body heat.
Down insulation is the best insulation for winter expeditions because of its excellent warmth-to-weight ratio. It is also highly compressible, which means that it can be packed down to a small size for easy transport. However, down insulation requires care because when it’s wet it loses its insulating properties. One way to avoid a damp and cold down bag is using a hydrophobic treatment, like Nikwax’s Down Proof, which is either applied in production or when washing the sleeping bag. Another way to keep your bag performing is to regularly hang it out to dry and air.
Down sleeping bags come in different fill powers, which refers to the loft or fluffiness of the down. The higher the fill power, the more air the down will trap (for a given weight of down) and the warmer it will be.
Synthetic insulation is made from man-made fibres, such as polyester. The insulation works by trapping warm air between the synthetic fibres. Synthetic insulation is less compressible than down insulation, so it requires more space in a backpack. However, it has the advantage of retaining most of its insulating properties even when wet, making it a durable and effective alternative to down insulation. Synthetic insulation is also easier to care for than down insulation - drying a down-filled bag after a wash often involves separating clumps of down by hand, whereas a synthetic bag goes straight on the washing line! Synthetic sleeping bags are typically more affordable than their down equivalents.
When choosing between down and synthetic insulation, consider the temperature and weather conditions you will encounter during your trip. If you are looking to invest in a longer-lasting sleeping bag or going on a Winter expedition where weight and warmth are critical, down insulation will be the better choice. However, if you are expecting wet or temperate conditions, camping in an easily accessible place or just looking for a more affordable option, synthetic insulation may be the way to go. Saying this, there are some synthetic bags that can rival even down for heat retaining power. Ultimately, the choice comes down to personal preference, specific needs and budget.
What do sleeping bag Season Ratings mean?
Season Ratings are used to indicate the time of year a sleeping bag is intended for. Ratings start from one season for the summer months all the way up to 4+ for extremely cold temperatures.
• 1 Season - Lightweight, compact and ideal for use in hot summer months (June-August) or when camping abroad in hotter climates.
• 2 Season - Ideal for use from late spring to early autumn, this is your typical family camping sleeping bag temperature range.
• 3 Season - For use from early spring until late autumn, and perhaps mild winter evenings. These bags are the sleeping bag recommended for school trips and expeditions, such as the Duke of Edinburgh.
• 4 Season - These thick, well-insulated bags are often filled with down to reduce pack size and weight and are designed for use during the winter when temperatures can drop below zero.
• 4+ Season - These sleeping bags, also known as expedition bags, are built for high mountain use where temperatures can get extremely low.
What do sleeping bag temperature/limit ratings mean?
In addition to a season rating, the warmth of a sleeping bag is usually indicated by three temperatures – Comfort, Limit and Extreme. These ratings are based on EN and ISO standards, which are both an attempt to standardize the way a sleeping bag’s performance is measured.
• Ignore the “Extreme” value, it is not a useful metric for selecting a sleeping bag. This number is solely about avoiding hyperthermia.
• The “Limit” indicates the air temperature at which a standard male can sleep for eight hours without waking.
• The “Comfort” value is the air temperature at which an average female can sleep comfortably through the night.
The ratings are useful for selecting and comparing sleeping bags. Unless you are a particularly cold or warm sleeper, we recommend using the “Comfort” value to determine the right sleeping bag for your trip.
What sleeping bag shape is right for me?
Sleeping bags come in all shapes and sizes. Different sleeping bag shapes cater to various requirements, for instance a mountaineer will value performance, weight and pack size, whereas a holiday camper may value space to stretch-out and comfort. The bag shape that is right for you depends on the kind of sleeper you are, the conditions you will use the bag in and your requirement for a small pack size.
• Rectangular - These sleeping bags are roomy and feel like a cosy duvet. They are ideal for camping in mild climates and for those who like the freedom to move around while sleeping. They are not as thermally efficient as other shapes as there’s more empty space to heat.
• Mummy - Mummy-shaped sleeping bags are designed to provide maximum warmth while minimizing weight. They have a tapered, body-shaped cut, resembling the shape of a mummy, with a narrower cut at the feet and wider at the shoulders. Mummy bags are perfect for cold weather camping or backpacking and are excellent heat retainers.
• Semi-rectangular or Modified Mummy - These sleeping bags strike a balance between the roominess of rectangular bags and the warmth of mummy bags. They have a slightly tapered shape but offer more space in the shoulder and leg area compared to traditional mummy bags. This design is a good compromise between comfort and thermal efficiency.
• Barrel - Barrel-shaped sleeping bags are wider in the middle and narrower at the feet and shoulders. This shape allows for more freedom of movement while providing reasonable warmth. Barrel bags are suitable for individuals who prefer a little more space without compromising too much on heat retention. They are also very suited to children.
• Double - Double sleeping bags are designed to accommodate two people. They typically feature a rectangular or barrel shape and have zippers on both sides for easy access. Double bags are perfect for couples or those who prefer sharing their sleeping space while camping.
What other sleeping bag features should I look for?
There are certain sleeping bag features that are worth keeping an eye out for. Baffle shape and construction are only a consideration for the experts; unless you understand what terminology like “shingled”, “stitched-through”, “offset” and “quilted” mean. For inexperienced buyers it’s best to rely on the temperature ratings.
A fitted footbox is a useful feature for minimising the amount of empty space at your feet and maximising warmth. However, when maximum performance isn’t a consideration, Mummy-style sleeping bags with this design may feel unnecessarily restrictive.
Draft collars/Neck baffles
Regular campers are often particular about the side of the bag the zip is on, especially for more fitted Mummy-style bags. Holiday campers might look for a bag with built-in pillows for added comfort and convenience.
Can I improve sleeping bag performance with a liner?
Yes. Sleeping bag liners are thin sheets of fabric that can be inserted into a sleeping bag to provide an extra layer of insulation, comfort, and protection. They are available in different materials such as silk, cotton, fleece, and synthetic fabrics, and different weights depending on your needs.
Using a liner can make your sleeping bag a few degrees warmer, making it better suited to colder temperatures. From a hygiene point of view, using a liner can help keep your sleeping bag clean and free of sweat and dirt. When choosing a sleeping bag liner, consider the fabric, weight, and size. It is important to choose a liner that fits your sleeping bag well to maximize its insulation and comfort benefits.
What sleeping mat do I need?
Your sleeping bag is just one part of your sleep system. The sleeping mat you place beneath your bag is an equally crucial piece of kit.
> Self-Inflating Mats
Self-inflating mats (SIMs) are filled with open cell foam which expands when the mat is unrolled and the valves opened, pulling in the air. The foam traps the air providing insulation and cushioning. Self-inflating mats come in many different shapes and sizes to help you find the right balance of insulation, packability and cushioning.
Pros of self-inflating mats:
• Require minimum effort to inflate
• Great warmth-to-weight ratio
• Easier to repair punctures than air-filled mats
• Plenty of options with high R-values
Cons of self-inflating mats:
• More expensive than and not as well-cushioned as air-filled mats
• Heavier and less compact than air-filled mats
> Air-Filled Mats
Air-filled or inflatable sleeping mats use air to provide cushioning and insulation from the ground beneath. More expensive versions can include synthetic insulation in the air baffles and reflective layers. They’re the ultimate in packable and lightweight sleeping, but they do require pumping up.
Pros of air-filled mats:
• Thicker and more padded than self-inflating mats - great for side sleepers
• Lightweight and packable
Cons of air-filled mats:
• Air circulating freely inside makes inexpensive options less warm than self-inflating
• Prone to punctures
> Closed-Cell Foam Mats
Lightweight, tough as old boots, and easily attached to the outside of a backpack, closed-cell foam mats are the preference of outdoors experts and expeditions. It is not unusual for these mats to be used in combination (this is known as “stacking”) with an inflatable mat.
Pros of closed-cell foam mats:
• Very lightweight
• Very durable – doesn't puncture
• No inflation required
• Often include reflective surfaces to reduce radiation heat loss
• A comfortable place to sit for a lunch break
Cons of air-filled mats:
• Comparatively low R-values
• Folded size is bigger than deflated inflatables
• Limited padding Vs inflatable mats
> Reflective Mats
It’s also important to mention reflective mats. These mats are designed to reflect back radiated heat. Typically made from a lightweight and durable material such as Mylar or aluminium foil, which is coated with a reflective surface. These mats can be folded for easy carrying. When temperatures are well below zero and the ground is frozen a reflective mat is a worthwhile investment. An emergency blanket (aka space or foil blanket) placed between a sleeping mat and bag also does the job.
What does sleeping mat R-number mean?
Sleeping mats and pillows have two main functions: insulation and comfort. Comfort is perhaps the more obvious benefit, as a sleeping mat provides cushioning over uneven ground and gives a more mattress-like feel.
But insulation from the ground, which conducts heat away from your sleeping bag at a faster rate than other forms of heat loss, is essential. The R-number or R-value indicates how effective a sleeping mat is at preventing heat loss to the ground through conduction.
An R-value between 1.0 and 2.0 is considered a summer sleeping mat. 2.0 to 3.0 covers most two and three season mats. A mat with an R-number of 4.0 or greater is considered a 4-season mat.
In general, self-inflating sleeping mats, which contain an open cell foam to aid inflation, have a R-number than inflatable mats.
How can I get the maximum cold weather performance from my sleeping bag?
It's important to keep in mind that the temperature rating provided by manufacturers is a guideline. The actual temperature you'll be comfortable in depends on many factors, such as your metabolism, the insulation of your tent, and the type of clothing you're wearing. When the temperatures catch you underprepared there are a number of things you can do to squeeze some more warmth from your sleep system.
Wear the right clothing – Thermal baselayers with long legs and arms, made from synthetic or merino wool fibres, are essential to a warm night’s sleep. Wear a warm (and breathable) hat and thermal socks to keep your extremities warm. Add midlayers when necessary.
But don't go overboard – It's important to let your core heat disperse through the bag to warm your extremities. Wearing a thick insulator will insulate your core, but there will less heat in the bag to warm your feet and toes.
Dry clothes - At the end of a long day it’s tempting to quickly strip down and jump into you bag. Before diving into your sleeping bag replace any damp clothes with dry layers.
Warm flask or hot water bottle (tight lid!) - On particularly cold nights a hot water bottle can add some welcome warmth. Make sure the lid is closed tightly and watertight so as not to scold yourself.
Eat plenty of calories – Your metabolism turns energy from food into body heat. Make sure your body has plenty of fuel by eating high energy foods before bed.
Loft your bag long before using it – When removing your bag from its compression sack give it a thorough shape to help loft the insulation. Then allow a little time for the fill to expand before getting in.
Keep your bag clean – A clean sleeping bag works
Always carry a liner – It's always a good idea to carry a liner. Microfleece liners can add a big boost to your sleep system’s warmth.
Emergency blanket – A space blanket is an essential survival tool which should
Fill dead space in your bag – using tools such space blankets
How should I store my sleeping bag?
Storing a sleeping bag properly will help maintain its performance and increase its lifespan.
Before storing your sleeping bag, it's important to clean and dry it thoroughly first. Follow the care instructions provided by the manufacturer for the best cleaning method. Special cleaning products from brands such as Nikwax and Grangers are available for down bags. Once the bag is clean, take the opportunity to make any necessary repairs.
To store your sleeping bag for an extended period, for instance during the winter months, it's best to avoid excessive compression. This can affect the insulation and loft of the bag over time. Instead, opt for a larger storage bag or hang the sleeping bag in a cool, dry place, away from direct sunlight, where it can keep its natural loft.
Storing sleeping mats is a similar process, depending on the type. Always clean and dry your mat before storing it to prevent mildew. Self-inflating mats benefit from being left unfurled with the valves open when storing for extended periods of time. Of course, if space is limited and it’s not possible to store the mat this way, then allow the mat to expand as much as possible. Remember that inflatable mats are prime for a puncture, take care to avoid sharp objects. It is fine to leave open and closed-cell foam mats rolled-up.
Protect it from damage: To prevent punctures or other damage, consider placing your sleeping mat in a protective cover or bag. This adds an extra layer of protection during storage, especially if you'll be storing it with other gear that could potentially cause damage.
