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Sleeping bags are designed to trap heat and provide warmth and thermal insulation. They are made of synthetic fabric or down insulation, with the former being the most common type of insulation used. The bags are designed to be lightweight and portable, and they can be closed with a zipper to form a tube. The bottom surface of a sleeping bag provides some cushioning, but a sleeping pad or camp cot is usually used for insulation as well. Sleeping bags come in various shapes, including rectangular, semirectangular, and mummy bags, with the latter being the most well-insulated and lightweight option. The insulation in the bag, combined with the construction method, determines the performance characteristics and insulation efficiency of a sleeping bag.
| Characteristics | Values |
|---|---|
| Purpose | To provide warmth and thermal insulation |
| Insulation | Synthetic or down |
| Cover | Water-resistant or water-repellent |
| Bottom surface | Provides some cushioning |
| Shape | Rectangular, semi-rectangular, or mummy |
| Construction | Baffles, tubes, quilting, shingling, layering |
| Materials | Nylon, taffeta, polyester, ripstop fabric, microfibers, Dryloft, Pertex, MemBrain |
| Performance | Weight, bulk, warmth, durability, water resistance |
| Features | Zippers, stash pockets, stuff sacks, storage sacks, sleeping bag liners |
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What You'll Learn
Sleeping bag anatomy
Sleeping bags are designed to trap heat that is radiated from the body, providing warmth and insulation. They are constructed with a variety of materials and design features to achieve this.
The outer shell of a sleeping bag is typically made from synthetic fabric, usually nylon, which is lightweight, durable, and water-resistant. The shell is often treated with a durable water repellent (DWR) finish to protect the insulation inside from dampness. The synthetic fabric is filled with synthetic insulation, usually polyester fibres, or goose/duck down. Down is made from the fluffy plumes that serve as an undercoat for geese and ducks, and the best down has the most plumes and least quills, providing higher fill powers. Down has a higher warmth-to-weight ratio than synthetic insulation, but it loses its insulating properties when it gets wet. Synthetic insulation is cheaper, easier to clean, and performs better when wet, retaining around 50% of its insulating ability.
The inner lining of the sleeping bag is constructed to be smaller in shape than the outer shell, allowing more natural space for the insulation to loft. The insulation is held in place by a system of baffles or tubes, which prevent the insulation from shifting and ensure even distribution. Vertical Thermal Channels (VTC) is a construction technique that uses vertical baffles to allow the insulation to rest closer to the user, improving comfort and reducing weight.
Sleeping bags come in various shapes, including rectangular, semi-rectangular or "modified mummy", and mummy. Rectangular bags are the most common for camping as they offer ample room to stretch out and can be fully unzipped to be used as blankets. Mummy bags are tapered from the head to the foot, reducing volume and improving heat retention. They often have an insulated hood, and some have a drawstring at the head to prevent the escape of warm air.
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Insulation and filling
The insulation in a sleeping bag is what provides the air space or loft necessary to minimise or slow down the heat loss from your body as you sleep. The best insulation will have the highest fill power, meaning less of it is needed to achieve the required loft for a given comfort range. Sleeping bags can be filled with either synthetic or down insulation. Synthetic insulation is the most common type and is made from poly-fibres, usually polyester fibres. Synthetic bags are cheaper, easier to clean, and require less care than down bags. They also perform better in humid or wet climates as they retain their insulating properties better than down when wet or damp. However, they are bulkier and heavier than down bags as they need more filling to be effective.
Down bags are made with the fine underfeathers from ducks or geese. Down has a very high warmth-to-weight ratio, meaning it is incredibly lightweight and can be packed down to a smaller volume than synthetic bags. Down bags are also longer-lasting than synthetic bags. However, down is more expensive and loses its insulating properties when it gets wet. For this reason, down bags are not ideal for humid climates.
The construction of the bag is also very important to its performance. The insulation must be held in place effectively between the outer shell and the inner lining to ensure the best insulation efficiency. With down bags, the down is usually held in place with a system of baffles or tubes, whereas synthetic insulation is secured through quilting, shingling, or layering. In both cases, the goal is to minimise the shifting of the insulation material, ensure even distribution, and prevent cold spots from forming.
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Construction and design
Sleeping bags are designed to trap heat that the human body radiates to the surrounding environment. They are constructed with an outer shell, insulation, and an inner lining. The outer shell is typically made of synthetic fabric, such as nylon, taffeta, or polyester fibres, and is usually water-resistant or water-repellent. The insulation is either synthetic, typically polyester fibres, or natural down, which has a higher warmth-to-weight ratio. Synthetic insulation is cheaper, easier to clean, and performs better when wet than down insulation, but down is lighter, compresses to a smaller size, and retains heat better. The inner lining is made of soft, warm materials.
The insulation in the bag, combined with the construction method, provides the airspace or loft necessary to minimise or slow the heat loss from the sleeper. The construction method must prevent the unplanned shifting of the insulation material, ensure even distribution, and prevent cold spots from forming. Baffles or tubes are used to hold down insulation in place, while synthetic insulations are usually secured via quilting, shingling, or layering. Box construction provides consistent down consistency and placement throughout the bag.
The basic sleeping bag design is a square blanket or quilt with a zipper on two or three sides, allowing the user to get into the bag and close it up. This design is roomy and works well for most camping needs but is inadequate for more demanding circumstances. Mummy bags, on the other hand, taper from the head to the foot, reducing volume and surface area, and improving heat retention. Mummy bags often have an insulated hood, and some do not unzip to the feet, as the zipper is a weak point in the bag's insulating qualities. Mummy bags are more expensive than lightly insulated rectangular bags and are designed for serious hikers and adventurers.
Sleeping bags come in various shapes, including rectangular, semi-rectangular or modified mummy, and double. Rectangular bags are the roomiest, followed by semi-rectangular, and then mummy bags. Rectangular and semi-rectangular bags are preferred by campers who want more room to stretch out and roll over, while mummy bags are used by hikers who want to cut weight and boost warmth. Double sleeping bags are designed for couples.
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Zippers and ventilation
A basic sleeping bag is a square blanket or quilt, fitted with a zipper on two or three sides, which enables users to get into the bag and then close it up. Mummy bags, which are tapered from the head to the foot end, usually do not unzip to the feet because the zipper is a weak point in any sleeping bag's insulating qualities. This design feature helps protect the feet, which are more vulnerable to heat loss than other parts of the body. Mummy bags also feature a drawstring at the head end to help prevent the escape of warm air.
A zipper with tape along its inside will prevent the bag from catching in the zipper. This is a useful feature when setting up camp in the middle of the night.
Sleeping bags are designed to trap heat that the body radiates to the surrounding environment. Ventilation is important to prevent a build-up of condensation. If necessary, bags should be hung out to air during the day if camping for more than a couple of nights. In warmer weather, sleeping bags can be unzipped and used like a blanket.
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Shapes and sizes
Sleeping bags come in a variety of shapes and sizes, each designed for different purposes. The three basic shapes are rectangular, semirectangular (or modified mummy/barrel shape), and mummy. Rectangular sleeping bags are the most common for camping as they offer ample room for legs and arms to stretch out. They can also be fully unzipped and used as a blanket, making them ideal for indoor use, caravanning, and summer camping. However, their heat retention capabilities are lower than those of mummy bags. Mummy bags, on the other hand, are designed to maximise warmth and minimise weight. They have a tapered shape, narrowing from the head to the foot, which reduces volume and surface area, improving heat retention. They also typically have an insulated hood, making them suitable for cold-weather use. Mummy bags do not unzip to the feet, as the zipper is a weak point in the insulation of any sleeping bag. The third shape, the semirectangular or modified mummy bag, offers a compromise between warmth and roominess.
Sleeping bags also vary in size, with some being large enough for two people. The size of a sleeping bag is an important consideration, as it needs to accommodate the user's body comfortably. Women's sleeping bags are designed to accommodate the average woman's body shape, and bags with a higher temperature rating will often have a snugger fit to improve warmth.
The weight of a sleeping bag is another critical factor, especially for backpacking and hiking. Lighter sleeping bags are typically more expensive, but they are crucial for adventurers who need to minimise weight and bulk. Synthetic sleeping bags tend to be heavier and bulkier than down bags, requiring more filling to achieve the same level of warmth.
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Frequently asked questions
The two main types of filling that sleeping bags are made from are man-made (e.g. polyester) and natural (down/duck/goose feathers). The outer shell of a sleeping bag is typically made of ripstop nylon or polyester.
First, choose the type of sleeping bag you want to make (mummy, rectangular, or semi-rectangular) and determine the dimensions. Then, select the fabric, zipper, insulation, and any additional features you want, such as a water-resistant coating, draft tubes, or a collar. Finally, follow a step-by-step guide to sew your sleeping bag together.
Consider the temperature rating, insulation type, bag shape, and extra features. If you are backpacking, choose a lightweight and packable sleeping bag that provides warmth. For car camping, you can prioritize warmth and space over weight and bulk.
