While the price tags can sometimes be daunting, a good quality sleeping bag can be thought of as an investment in your comfort. When you crawl into the soft warm bag at the end of a miserably wet day hiking, you will not be regretting the purchase. Getting a good night sleep can make all the difference in the outdoors, and in more extreme environments a sleeping bag can be as much a life saving device as a climbing rope or helmet. Skip down to the Quick Guide section of this article for a fast explanation of common bag types and warmth ratings, giving examples of their common uses. The later section goes into some more technical info on the features of modern sleeping bags.
Quick Guide: Buying a Sleeping Bag
A few common outdoor activities are listed (from warmest to coldest), with an appropriate style of sleeping bag and price range listed to match.
Activity: School trips, car camping, backpacking, children
- Fill: Synthetic
- Budget: $150 - $250
- Weight range: 800 – 1300grams
- Features: Machine washable, budget friendly, low maintenance
- Example Products: Mont Evo Series
Activity: 3 season travelling, car camping, backpacking
- Fill: Down
- Budget: $300 - $500
- Weight range: 900 – 1200grams
- Features: Comfortable rectangular shape, full zip folds out like a blanket
- Example Products: Exped Comfort Series, Mont Zodiac Series,
Activity: 4 season Sydney hiking, adventure travel
- Fill: Down
- Budget: $400 - $700
- Weight range: 700 – 1100grams
- Features: Tapered cut reduces weight and packed size and warms more effectively
- Example Products: Exped Lite Series, Exped Comfort Series, Mont Tapered Rectangular Series, Mont Helium Series
Activity: Australian Snow Trips, New Zealand Mountaineering
- Fill: Down
- Budget: $700 - $1000
- Weight range: 1100 – 1600grams
- Features: Technical baffles for maximum warmth, water resistant shell materials and fill treatments
- Example Products: Mont Specialist Boxfoot Series
Activity: Himalayan Mountaineering, Arctic Travel
- Fill: Down
- Budget: $1000
- Weight range: 1600+grams
- Features: Highest loft down fills, oversized bags allow room for boots and down clothing inside.
- Example Products: Mont 8000 Series
Insulation Material: Down versus Synthetic Fill
Sleeping bags keep you warm by preventing your radiant body heat from escaping into the air around you. A fibrous fill substance inside the baffles of a sleeping bag achieves this phenomenon, and the two types of fill available are down (fine goose or duck feathers) or synthetic fibres.
Down Sleeping Bags
Down sleeping bags are the predominant option on the sleeping bag market. They have the highest insulation capacity to weight ratio of sleeping bag fills, that is to say that down is both the warmest and lightest fill material. Both goose and duck down is used in sleeping bags, and while it is often perceived that goose down is superior to duck, lately there have been higher quality advances in duck down so this is not a hard and fast rule any more. What is more important is the “loft” rating. Down quality is measured in “Loft” or “Fill Power”, a measurement of the volume of down divided by its weight. The higher the loft, the more air the down can trap next to your body, and hence the warmer the sleeping bag will be. Higher loft down is also lighter and softer than lower loft down, and will compress to a smaller size when packed. Loft of less than around 600 is considered low quality and will be relatively heavy. Loft ratings of 600 to 850+ are very good quality, and will be lightweight to carry.
The main disadvantage of down as a sleeping bag insulation material is that it loses thermal insulation capacity when wet. Manufacturers combat this problem with the introduction of water resistant or fully waterproof shell materials on their sleeping bags, or a chemical treatment within the down itself to make it repellent to moisture. In most cases these treatments are more than adequate, and a down sleeping bag is still the best choice for most trips. For some specialist purposes where a wet sleeping bag is inevitable however (sleeping in a snow cave for example), a synthetic fill sleeping bag may be a better choice. Down sleeping bags are also difficult to wash, so it’s a good idea to use a lightweight sleeping bag liner to prevent the sleeping bag being soiled by the sweat from your day’s adventures.
Synthetic Sleeping Bags
Synthetic fibre sleeping bags trap radiant heat within the bag the same as a down bag, but have the advantage of retaining some insulation value when wet. Sleeping in a damp sleeping bag is never going to be a riot, but in cold weather it can be a necessary evil. Synthetic sleeping bags are far cheaper than down bags, but are heavier and bulkier for the same warmth rating. Synthetic bags are machine washable, so are a great choice for kids on school trips or family camps where they are inevitably going to get dirty.
Sleeping Bag Warmth
Sleeping bags will usually come with the manufacturer’s recommended warmth rating. Sometimes this will be a range such as “0 to 5 degrees”, or sometimes a series of values such as “Comfort 0 degrees, Lower Limit –7 degrees, Extreme –15 degrees”. Some manufacturers will have their bags independently tested to a particular standard (EN 13537 is often used), and some may advertise their own opinion of the rating.
The most important thing to remember when assessing the warmth of a sleeping bag is that the warmth of a bag is subjective, and a myriad of factors will ultimately determine if you are warm in a sleeping bag. Conditions like the air and ground temperature, your metabolism, size, gender, hydration level, fatigue level and sleeping mat type will all play a part. Good quality brands will be pretty close with their ratings, but do consider them a guide and not a steadfast rule.
To make your own assessment in the warmth of a bag, consider a combination of the following factors:
Down Loft and Weight
The “puffier” a bag looks, the more air it will trap next to your body and the warmer it will be. We know that a higher loft rating will be warmer than a lower one, but also look at the “weight” of down put into the sleeping bag, i.e; a sleeping bag with 500grams of 800 loft down will be warmer than a bag with only 400grams of 800 loft down.
Bag Shape and Size
The less air inside the bag that your body has to heat, the warmer a sleeping bag will be. A rectangular sleeping bag is roomy and comfortable, but the “dead air” spaces that your body doesn’t fill up will make the bag colder. A “mummy”, or tapered sleeping bag is typically the warmest shape for a bag, as they minimises excess space. Even a tapered sleeping bag that is too long or wide for you will be inefficient, so sleeping bags typically come in standard or XL sizes, and some models will have a small or womens cut as well. A womens sleeping bag typically uses the same fill weight of down as the equivalent standard bag, but has it packed into a bag two baffles shorter, making it even warmer for its volume. For snow trips, size a bag a little bigger than usual to allow room to wear extra down clothing inside the bag, and store other good like your boots in the end.
Thin nylon shell materials will result in the lightest weight bags and will be the most breathable, but will potentially also allow the greatest heat loss. High denier microfiber nylons and polyesters are heavier, but are more durable, have lower heat loss and can be made highly water resistant. This is by far the most common material for cold weather sleeping bags. Laminated waterproof / membraned sleeping bags are less common. They have good heat retention, but are very heavy, have the lowest breathabilty, and are typically expensive and specialist in their use.
Other Heat Retention Features
Anything that keeps air in the sleeping bag will help to keep you warm. A closable draft baffle around the neck makes a huge difference to the warmth of a bag, as similarly does a good fitting hood. A draft tube running down the inside of the zip will help stop air escaping, and a “box foot” shape at the end of a bag will give room for your feet to stop them compressing the down and lowering its insulation capacity.