Sleeping bags

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Sleeping bags and Liners

A comfortable, warm sleeping bag is essential for overnight bushwalking.

Sleeping bag performance is determined by the type and quality of the ‘fill’ (insulating material) used. Goose or duck down are the most common fills used in sleeping bags for bushwalking or ski touring.

Down is the light, fluffy plumage that grows under feathers of geese or ducks and provides warmth by creating pockets of air that trap heat.

Fill power is the rating system that measures the volume for a given weight of down when uncompressed. Higher fill power numbers reflect better quality down which traps more air to provide a better warmth to weight ratio.

Down is exceptionally resilient and capable of being repeatedly compressed into a stuff sack without compromising its ability to provide warmth. A quality down sleeping bag can be expected to last more than a decade.

Good quality down-filled bags are expensive, but very warm. Synthetic-filled bags are cheaper to produce in comparison, but are heavier and more bulky.

Manufacturers of synthetic fill sleeping bags have developed proprietary fill products, but two types are more common:

• Short staple fibres imitate the plume structure of down and compress well, but break down sooner when compressed multiple times. 
• Continuous filaments weave long filaments of variable diameter to create a durable, high-loft insulation, but are less compressible.

Other factors that affect a sleeping bag’s performance are the bag’s shell materials, its shape and other design elements.

Down vs Synthetic fill

Down fill

Advantages

• Provides best warmth to weight ratio.
• Compress much smaller than synthetic fill bags and are therefore more space efficient in the pack.
• Down fill is more durable.
• Down retains a more consistent level of warmth for a longer period of time.
• A down bag will last for decades if it is well looked after and properly cleaned occasionally.

Disadvantages

• Down bags are expensive.
• Performance when wet is significantly diminished.
• Take a long time to dry if they get wet.
• Must be aired after every trip and, if possible, during the trip.
• Require a special ‘down soap’ for washing and are difficult to wash and dry

Synthetic fill

Advantages

• Considerably cheaper than a down bag.
• Provide better insulation when wet.
• Dry faster than down bags.
• Easier to wash and don’t require special soap.
• Best used in moderate rather than cold conditions and where the possibility of getting wet is high.

Disadvantages

• Heavier and bulkier than a comparable down bag.
• Shorter lifespan than a down bag.  Once synthetic fill starts breaking down, the bag cannot be rejuvenated.

Considerations when selecting a sleeping bag

Temperature rating

Manufacturers’ temperature guides are indicative. People sleep comfortably at different levels of warmth. It is important to select a sleeping bag that matches your needs.

Sleeping bag temperature ratings attempt to specify the lowest temperature at which a bag is designed to keep an ‘average sleeper’ warm (e.g. -5C). Note that these ratings may vary between manufacturers.

Choose a sleeping bag with a rating that is 5 to 10C lower than the expected minimum temperature of use.  For example, for -5C temperatures typically expected for snow camping in Australia, choose a bag with a rating of -10 to -15C.

To regulate comfort, extra clothing or a liner can provide added warmth if needed. 

Bag weight

• Type of insulation, temperature rating, materials and bag shape are the main factors.
• Compare bags of similar temperature ratings when comparing the actual bag weight.
• More efficient insulation delivers greater warmth for less weight.
• Higher quality sleeping bags weigh less and cost more.

Bag shape and size

Sleeping bags come in different shapes and a variety of lengths and widths.

• Rectangular bags have a large internal space, come with or without a hood and are only usually used for general camping as they are large and heavy.
• Mummy shaped bags have a very snug fit with little spare space inside to trap warm air close to the body, thus providing warmth with the lightest weight.
• Tapered bags improve thermal efficiency due to less internal space needing to be warmed and are less restrictive than mummy-shaped bags.

Other design features

• Hoods offer added warmth. They can be flat or three dimensional in design and use draw cords to cinch the hood closer around the head to reduce heat loss.
• Draft tubes are insulation-filled tubes on the inside of a bag behind the zipper to minimise heat loss.
• Neck/chest collars are insulation-filled tubes located around the top of a bag to prevent warm air from escaping and can usually be tightened for a snug fit.
• Baffles are internal walls made of very light material sewn between the inner and outer shell material to hold insulation in place. More expensive down bags have elaborate baffle systems to increase efficiency and warmth.
• Box or shaped foot is usually found on tapered and mummy-shaped bags to provide space for the feet.
• Sleeping bag outer shells are usually ripstop nylon or polyester. Many shell fabrics are also treated with a water repellent finish to prevent moisture soaking through and dampening the fill. More expensive bags may have a vapour membrane fabric (e.g. Dryloft ™)
• Lining fabrics may have a softer texture.
• Sleeping mat integration. Some bags have a sleeve on the underside to insert a sleeping mat. Some have loops to secure the mat to the bag. The pad becomes an integral part of the sleeping system in order to save some weight, but these designs are  not popular due to being unable to roll over with the bag and the tendency to have cold spots.
• Wet conditions Synthetic fill can retain its loft and some warmth even if wet. A down-filled bag is ineffective if it gets wet. Most manufacturers now use down treated with water-repellent to absorb less moisture, dry faster and retain loft, which can improve water-resistance.  These treatments can lose their effectiveness over time.
• Double bag Some rectangular bags of the same brand/type can be zipped together to form a double sleeping bag.

Responsible Down Standard

Down used in sleeping bags is a by-product of raising geese and ducks for meat.

There is an independent voluntary global standard to ensure ethical treatment of these birds. It aims to ensure that down and feathers come from birds that have not been subjected to unnecessary harm.

Many manufacturers certify that their down is sourced from traceable, verifiable farms that follow best practices and standards for animal welfare.

Cleaning and storage

• • Only wash sleeping bags when absolutely necessary. Repetitive washing contributes to fill material and water repellent treatments deteriorating.
  • Use specialised down cleaner to wash down bags.This will restore water repellency and retain loft.
  • Squeeze as much water out as possible when washing a down bag before lifting the bag to avoid down clumps tearing the delicate baffles.
  • Wash synthetic bags in a large front-loader machine using very mild detergent and warm water on a gentle cycle.
  • Always air a sleeping bag before storing it.
  • Store bags semi-lofted in a large bag (not in the stuff sack) to avoid crushing fibres of  synthetic bags or reducing the loft of down bags.
  • Store in a dry environment to prevent mould.

Compression sacks

• Compression sacks provide straps to allow further compression of a sleeping bag. 
• Most good quality down sleeping bags come with a compression sack.
• The small amount of weight it adds is worthwhile for the space gained.
• Some have a panel of breathable fabric to vent air as the bag is compressed.

Stuff sacks

• A lightweight, waterproof seam sealed sleeping bag stuff sack with a dry bag closure will keep a sleeping bag dry and clean when carrying it in a pack. 
• Stuff sacks cannot compress a sleeping bag to the same extent as a compression sack so it will take up more space in a pack.

Sleeping bag liners

• Sleeping bag liners are lightweight and compact sacks used to line the inside of the sleeping bag.
• Liners protect the sleeping bag from body oils and sweat thereby keeping the bag cleaner and prolonging its life. It is much easier to wash a liner than a sleeping bag
• They are usually rectangular and come in different lengths. Mummy-shaped liners are available to fit that style of sleeping bag. Some have stretchy sides allowing for greater movement, others have a hood.
• Liners add warmth to the sleeping bag in cold weather thereby increasing the range of temperatures in which a sleeping bag will be comfortable.
• Liners can be used by themselves in hot weather with the sleeping bag used as a doona if needed.

Types of liner materials

• Silk is very lightweight, compact, absorbent and breathable in warm weather, but also adds warmth in cooler weather.
• Synthetic (e.g. CoolMax™) liners are designed for warm or humid conditions using moisture wicking and breathable fabric.
• Insulated (e.g. Thermolite™) liners are soft and the stretchy fabric made of hollow core fibres to trap heat. The tapered design, box foot and drawcord hood adds a significant amount of warmth.