You’ve probably heard that your shelter, your sleep system, and your pack constitute the Big Three. If you want to significantly reduce your pack weight, you’d probably want to start not with reducing the weight of your hiking shoes of clothes but rather with reducing the weight of your Big Three.
The sleep system is a combination of pad, bag or quilt, clothing, and sometimes, bivy bag that you surround yourself with to keep warm at night. Keeping warm at night is essential for enjoyable backpacking. Nothing destroys the pleasure of a trip like shivering through the night in an inadequate sleeping bag. A sleeping bag reduces convective heat loss by trapping body-warmed air in tiny pockets so it does not dissipate freely into the atmosphere. These air pockets are formed by high-loft insulation like goose down or synthetic fill, which is sandwiched between two layers of fabric. The warmth of a sleeping bag is a function of its insulation, shell fabrics, style, and construction.
Your sleeping pad should be an integral part of your sleep system. It’s at least as important as your bag because no sleeping bag can provide good insulation between you and what you’re lying on. In our next post, we’ll talk more about sleeping pads.
There are a variety of factors to consider when evaluating sleeping bags. Among them:
- Type of insulation.
- Sleeping bag size. (Extra volume around your body means more space to heat.)
- Sleeping bag weight.
- Weather conditions like wind or humidity.
- How warm you happen to sleep on any given night. (Some people tend to be warmer sleepers than others, and most people vary in how warm they’ll sleep on any given night.)
- Price considerations.
Types and important features of sleeping bags
Although there are many models, choosing a sleeping bag should be relatively easy. The biggest decision is the kind of insulation or fill, followed by how warm a bag you need and how compact it is. The ideal bag would be lightweight but very warm, low in packed bulk, durable, nonabsorbent, quick-drying, warm when wet, comfortable, and compact sleeping bag. Unfortunately, this ideal doesn’t yet exist, so compromises have to be made in terms of which properties are most important. The basic choice is between synthetic fibers and waterfowl down.
When you buy a sleeping bag, you will be given a choice of either down-fill or synthetic insulation.
Synthetic fills cost less than down, are easy to care for, and resist moisture. But they are not “warm when wet”, as some manufacturers claim. What matters is how fast something dries, and synthetic fills dry fairly quickly since they are virtually nonabsorbent. A wet synthetic filled bag will start to feel warm in a comparatively short time compared with a wet down-filled bag, as long as it’s protected from rain and wind. You can’t sleep outside in a downpour in a synthetic-filled bag and stay warm, however.
The disadvantages of synthetic fills compared with down are shorter life, less comfort over a wide temperature range, more packed bulk, and greater weight for the same warmth.
Down is the lightest, warmest, most comfortable and most durable sleeping bag fill. No synthetic yet comes near down for packability, low weight, and warmth. Down is the fluffy under plumage of ducks and geese and consists of thin filaments that trap air and thus provide insulation. Down recovers well from compression and goes on doing so for a long time, hence the good durability. Down from geese is generally warmer than down from ducks. The more volume a given amount of down can fill, the higher its quality, because the thickness, known as loft, determines the warmth. Measuring the volume filled by an ounce of down determines the fill power. Down of 500 to 550 fill power is the least expensive but provides less warmth for the weight than down with higher fill power. The warmest, lightest, and most expensive bags are filled with down of 750 to 900 fill power.
One of the biggest downsides of down is that it absorbs a great deal of moisture, and it takes a long time to dry. Drying a sodden down bag outside in wet weather is practically impossible. But keeping down dry need not be difficult or a chore, and it’s harder to get down wet than many people think. Just pack your down bag in a waterproof stuff sack and try to sleep in a tent or under a tarp when it rains. Following these simple rules should be enough to keep your down bag away from moisture. It’s also wise to air down bags occasionally to remove any moisture picked up from humid air or from your body.
There’s currently no legal standard, but sleeping bags labeled as “down” should be at least 75 percent down. The figures are often expressed in the form 85/15 or 85:15 for 85 percent down, 15 percent feathers.
Sleeping bag shells need to be lightweight, hardwearing, breathable, resistant to wind and water, nonabsorbent, and quick drying. Nonwaterproof shells are highly breathable, allowing body moisture through very quickly, which keeps the fill dry and ensures good loft. They are moisture-resistant and dry quickly, but they won’t keep rain out for long. Waterproof breathable shell fabrics are waterproof, but bags made from them usually aren’t, since water can enter through the seams unless they are sealed, which is rare.
The first step in picking a sleeping bag is deciding upon a temperature rating. Just as there is no such thing as a four-season tent, there are no year-round sleeping bags. In general, for backpacking in spring, summer, and fall, you will be best served by a bag rated to -5-7°C and weighing no more than 1500 g (if you prefer lightweight packing, then your compact sleeping bag would probably be up to 30-40% lighter). This is warm enough for chilly nights yet not too hot when opened up like a blanket. If the temperatures really drop, you can augment the rating by wearing additional clothing. You can also augment the warmth of your sleeping bag with thermal liners that can boost the rating by a few degrees Celsius.
One of the most widely used standards designed to standardize the temperature ratings on sleeping bags is called EN 13537. The standard measures four temperature ratings – maximum, comfort, lower limit, and extreme. Two of these ratings are actually much more important than the rest, namely the Comfort rating and the Limit rating. The Comfort temperature “is calculated for a standard woman (25 years old, 60 kg, 1.60 m tall, body surface 1.62 m2) who does not feel cold and does not shiver (in relaxed position)Ó, while the Limit temperature Òis calculated for a standard man (25 years old, 70 kg, 1.73 m tall, body surface 1.83 m2, metabolic production 46 W/m2, thermal performance 82.8 W.) when he fights against cold curled into ball inside of the sleeping bag but he is in thermal balance and he does not shiver.” while the Limit temperature “is calculated for a standard man (25 years old, 70 kg, 1.73 m tall, body surface 1.83 m2, metabolic production 46 W/m2, thermal performance 82.8 W.) when he fights against cold curled into ball inside of the sleeping bag but he is in thermal balance and he does not shiver.” The ratings assume you have an insulated pad, a base layer set, a pair of socks and a warm hat. If you stray from this recipe you are either giving up temperature or adding temperature depending on which way you stray.
Temperature ratings are highly subjective, since many factors affect them, including your gender and age, metabolism and hydration, level of fatigue, acclimatization to outside temperatures, the thermal efficiency of your sleeping pad, air humidity, wind speed, humidity of insulating filling of your sleeping bag etc. Perception of thermal comfort depends on the personal dispositions of an individual and his cold hardiness etc.
Types of sleeping bags
There are several types of sleeping bags:
- Rectangular sleeping bags
The most traditional type of sleeping bags, preferred by those who like to have a lot of room when they sleep. Suitable for warm-weather camping, this kind of bag is the most economical. Many camping stores offer rectangular sleeping bags in a single or a double size. For that reason, you will find that a double rectangular sleeping bag is the perfect option for couples who go camping. Additionally, some rectangular sleeping bags will allow you to connect multiple sleeping bags together. A downside of a sleeping bag that is too wide or too long is that it won’t keep you as warm as one that fits properly, and the weight will be more than you need to carry.
- Mummy sleeping bags
Compact sleeping bags that fully enclose the body and head in a cocoon-like wrap of insulation. The integrated hood further minimizes drafts, and the tapered design eliminates dead air spaces inside the bag that otherwise would have to be kept warm. It’s the standard shape for high-performance, lightweight sleeping bags and is very efficient at heat retention. Mummy sleeping bags are all constructed with the same types of insulation, shell fabrics, and construction techniques, often at the same factories in Asia. Among the downsides of mummy sleeping bags are the limited venting features and the limited space you have inside the bag (it may be really claustrophobic inside).
They can open completely like blankets and are similar to those found on household beds. But they are constructed from outdoor-worthy fabrics and insulations, and many feature a foot box that extends up to the knees or lower thighs. This kind of sleeping bag ensures versatility, warmth, and comfort.
- Wearable sleeping bags
They are multifunctional: they serve as both a sleeping bag at night and insulated clothing in camp or during cold midday stops. They sound great in theory, but the extra build will offset some of the weight savings, and sometimes products that strive to be everything are good at nothing.
When you’re looking for a sleeping bag, try to find the perfect balance between warmth, weight, comfort, and functionality. If you want to travel light, a compact sleeping bag is a natural choice. A down or synthetic-fiber mummy sleeping bag is usually necessary for comfort at temperatures below freezing. A bag with a full zipper is more versatile because it is comfortable at cool, high altitudes and in warm, low country. Unfortunately, sleeping bags do not have removable layers of insulation so you need some experience to identify what kind of sleeping bag you will need in different weather conditions.