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Kids camping

Kids camping (PeopleImages, iStockphoto)

STEM in Context

How Do Sleeping Bags Work?

Aisha Mohamed & Let's Talk Science

Summary

How do our bodies get cold? How do sleeping bags keep us warm?

Have you ever gone camping? Have you ever tried to stay warm in the winter? If you said yes to either question, you’ve probably used a sleeping bag or a winter coat. Let’s look at how our bodies get cold. Then, let’s look at how sleeping bags and winter coats keep us warm.

What is the ideal temperature for our bodies?

As our cells burn energy, our bodies produce heat. Our blood transfers this heat around so that overall our body stays in an optimal temperature range. This range is normally between 36.1 degrees celsius (97 degrees fahrenheit) and 37.2 degrees celsius (99 degrees fahrenheit). Our bodies need to be in this temperature range to work properly . The process of keeping a body within its optimal temperature range is called thermoregulation.

How do our bodies lose heat?

Why do we get cold? This happens if the temperature of our skin is higher than the temperature of our surroundings. In these cases, our bodies can lose heat. 

 

There are three ways heat transfer can happen:

  1. Thermal radiation

  2. Conduction

  3. Convection

 

Thermal radiation is the transfer of energy through electromagnetic (EM) waves. Many objects can transfer heat through thermal radiation. Some examples are:

1. A hot campfire

2. A glowing heating element on the stove 

3. The Sun 

Thermal image of a woman on a couch. White parts are the hottest and black spots are the coolest. Notice how the heat radiates away from the body to the couch
Thermal image of a woman on a couch. White parts are the hottest and black spots are the coolest. Notice how the heat radiates away from the body to the couch (Source: vansmuk via iStockphoto).

Conduction happens when solids come into contact with one another. Heat energy will always move from a warmer object to a cooler one. This is because a warmer object has quickly vibrating molecules.  When they touch a cooler object, the molecules transfer energy. This makes the cooler molecules vibrate more quickly, and the object heats up. For example, have you ever sat on a cool couch? Did you notice how the seat was much warmer when you stood up? That’s because the heat from your skin was transferred to the couch through vibrating molecules.

Convection is the movement of molecules within fluids (liquids and gases) caused by heat transfer. It happens when liquid or gas molecules move apart. When warmer air or water moves away from a source of heat, it carries energy with it. For example, when you heat water in a pot on the stove or in a kettle, the hot water rises. Similarly, when your skin is warm, the nearby air moves away from you.  

Boiling water in a kettle on the stove is a good example of the heat transfer processes of conduction, convection and radiation
Boiling water in a kettle on the stove is a good example of the heat transfer processes of conduction, convection and radiation (Let’s Talk Science based on an image from inkoly via iStockphoto ).

How can we keep our bodies warm?

So how can we protect our bodies from heat loss in cool places? One important way is to surround ourselves with insulation. Insulation traps a layer of warm air around your body. This makes the temperature of the air next to your skin warmer. As a result, you don’t lose as much heat.  

Sleeping bags and winter coats both use insulation. They contain materials with insulating properties. The two main ones used in sleeping bags are feather down and synthetic insulation. Feather down is often just called “down.”

Cross-section of a sleeping bag showing the air and the feather down
Cross-section of a sleeping bag showing the air and the feather down (© 2019 Let’s Talk Science).

What is down insulation?

Down insulation is made from the small, fluffy feathers found on birds. The down in sleeping bags usually comes from ducks or geese. Down protects you from heat loss by trapping warm air amongst its fine fibres.

 

Did you know?

Female birds like ducks and geese line their nests with down feathers plucked from their own chests!

Close-up photo of a down feather
Close-up photo of a down feather (Source: Yoky [CC BY-SA 4.0] via Wikimedia Commons ).

Down insulation has the advantage of being very warm. By weight, it is warmer than synthetic insulation. It can be packed very tightly in coats and sleeping bags to provide warmth without being bulky. A synthetic sleeping bag might be just as warm, but it will be much bulkier! If you take care of down properly, it can last a very long time. 

But there are some challenges with down insulation. First of all, it is very expensive. Secondly, it loses its ability to provide warmth when it gets wet. It also takes a long time to dry, which can be a problem if it rains on your camping trip! When down gets wet, the feathers all stick together. When this happens, they can no longer trap warm air between their fibres.

But down insulation comes with some ethical challenges.The feathers used in down insulation come directly from animals. Some people have concerns about these animals’ living conditions. 

Also, down jackets are very expensive. A lot of people simply can’t afford them. 

Did you know?

A school in the UK banned Canada Goose jackets. These jackets are expensive, and school officials worried that they highlighted the economic differences between students.

What is synthetic insulation?

Synthetic insulation is made of polyester fibers that are arranged to mimic down fibers. It is much cheaper than down insulation. It has the ability to provide warmth even when it’s wet, which is very useful for wet and cold climates. This is because the fibres do not stick together when wet the way that down fibres do.

But synthetic insulation has disadvantages, too. It is not as durable as down insulation.  The materials will eventually break down no matter how well you take care of them.  

Did you know?

On average, a down sleeping bag lasts about 10 years. A synthetic sleeping bag last about 3 years.

Astronaut Samantha Cristoforetti of the European Space Agency (ESA) is seen inside of a sleeping bag in her personal crew quarters on the International Space Station
Astronaut Samantha Cristoforetti of the European Space Agency (ESA) is seen inside of a sleeping bag in her personal crew quarters on the International Space Station (Source: NASA via Wikimedia Commons ).

As you can see, there is a lot to consider when buying your next jacket or sleeping bag!

Starting Points

Connecting and Relating
  • Do you have a sleeping bag? What type of insulation does it have inside? 
  • Does anyone in your family have a down sleeping bag, duvet or winter coat? What do they like about it? Is there anything about the features of down they don’t like? 
  • Does it matter to you if the insulation in your sleeping bag is natural or man-made? Why or why not? 
  •  
Connecting and Relating
  • Do you have a sleeping bag? What type of insulation does it have inside? 
  • Does anyone in your family have a down sleeping bag, duvet or winter coat? What do they like about it? Is there anything about the features of down they don’t like? 
  • Does it matter to you if the insulation in your sleeping bag is natural or man-made? Why or why not? 
  •  
Relating Science and Technology to Society and the Environment
  • Why are sleeping bags made with synthetic insulation less costly to manufacture that those made with goose down? 
  • Years ago sleep comforters used to always be made with feathers or down as insulation. What factors influenced the development of synthetic alternatives to feathers and down?  (e.g., allergies to feathers and down, decreases in geese being farmed, increase in the size of the market, scientific developments in materials science, etc.)
  • How is polyester made? How do polyester and down compare in terms of their environmental impacts? 
  •  
Relating Science and Technology to Society and the Environment
  • Why are sleeping bags made with synthetic insulation less costly to manufacture that those made with goose down? 
  • Years ago sleep comforters used to always be made with feathers or down as insulation. What factors influenced the development of synthetic alternatives to feathers and down?  (e.g., allergies to feathers and down, decreases in geese being farmed, increase in the size of the market, scientific developments in materials science, etc.)
  • How is polyester made? How do polyester and down compare in terms of their environmental impacts? 
  •  
Exploring Concepts
  • How does the down or synthetic fibre in a sleeping bag keep you warm? 
  • What is heat transfer? What conditions could increase heat transfer when you are sleeping outside? What can decrease heat transfer? 
  • What is the difference between down and feathers? What different functions do down and feathers perform for the goose when they are on the goose’s body? Do ducks and geese use down and/or feathers in other ways?  
  •  
Exploring Concepts
  • How does the down or synthetic fibre in a sleeping bag keep you warm? 
  • What is heat transfer? What conditions could increase heat transfer when you are sleeping outside? What can decrease heat transfer? 
  • What is the difference between down and feathers? What different functions do down and feathers perform for the goose when they are on the goose’s body? Do ducks and geese use down and/or feathers in other ways?  
  •  
Nature of Science/Nature of Technology
  • What ethical reasons might a person have for preferring to own a down-insulated sleeping bag? How about a synthetic sleeping bag? 
  • Do you think it is right that the UK school that was mentioned in the article banned students from wearing Canada Goose jackets because of their price? Why or why not? 
  •  
Nature of Science/Nature of Technology
  • What ethical reasons might a person have for preferring to own a down-insulated sleeping bag? How about a synthetic sleeping bag? 
  • Do you think it is right that the UK school that was mentioned in the article banned students from wearing Canada Goose jackets because of their price? Why or why not? 
  •  
Media Literacy

  • Have you seen any advertisements for down sleeping bags or winter coats? How do the ads present the features and advantages of these down products? Do these ads seem to be targeting a particular type of buyer? Explain. 

Media Literacy

  • Have you seen any advertisements for down sleeping bags or winter coats? How do the ads present the features and advantages of these down products? Do these ads seem to be targeting a particular type of buyer? Explain. 

Teaching Suggestions
  • This article can be used for teaching and learning in Math & Physics and Health & Human Body related to thermal energy sources and heat transfer. Concepts introduced include sleeping bags, insulation, heat transfer, feather down, synthetic insulation and polyester. 
  • After reading this article, teachers could have students consider the positive and negative aspects of using down in a sleeping bag using a Pros & Cons Organizer learning strategy. Ready-to-use Pros & Cons Organizer reproducibles are available in [Google doc] and [PDF] formats. 
  • To consolidate learning, teachers could have students complete a Concept Definition Web learning strategy for the concept of insulation. Ready-to-use Concept Definition Web reproducibles are available in [Google doc] and [PDF] formats. 
  • To extend learning, teachers could have students conduct some additional research on synthetic vs natural down insulation and then complete a Venn Diagram to compare and contrast the features of each. 
  • For a media arts extension, students could create an advertisement or infographic presenting the key features and science behind their sleeping bag of choice (down or synthetic). 
  •  
Teaching Suggestions
  • This article can be used for teaching and learning in Math & Physics and Health & Human Body related to thermal energy sources and heat transfer. Concepts introduced include sleeping bags, insulation, heat transfer, feather down, synthetic insulation and polyester. 
  • After reading this article, teachers could have students consider the positive and negative aspects of using down in a sleeping bag using a Pros & Cons Organizer learning strategy. Ready-to-use Pros & Cons Organizer reproducibles are available in [Google doc] and [PDF] formats. 
  • To consolidate learning, teachers could have students complete a Concept Definition Web learning strategy for the concept of insulation. Ready-to-use Concept Definition Web reproducibles are available in [Google doc] and [PDF] formats. 
  • To extend learning, teachers could have students conduct some additional research on synthetic vs natural down insulation and then complete a Venn Diagram to compare and contrast the features of each. 
  • For a media arts extension, students could create an advertisement or infographic presenting the key features and science behind their sleeping bag of choice (down or synthetic). 
  •  

Learn more

Stay Warm with Thermal Insulation (2017)

Easy experiment from Svenja Lohner exploring the properties of heat transfer.

'Ethical down': is the lining of your winter coat nothing but fluff? (2016)

Article by Oliver Milman from The Guardian discussing the ethical and economical concerns of using down products.

What is Hydrophobic Down and is it any good? (2014)

Video (6:40 min.) from GO Outdoors TV comparing natural down and down that’s been treated with a hydrophobic (water-resistant) coating.

References

Abedi, M. (2018, November 16). Canada Goose jackets banned by U.K. school for being too expensive. Global News.

Rosenthal, Martha S. (n.d.). Thermal regulation. Biology Reference.