How Do Sleeping Bags Work?

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 

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.  

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.”

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!

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.

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