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How Do Sleeping Bags Actually Work?

If you have ever had a sleeping bag you will always be amazed at how well they work. If you are in freezing conditions they seem to keep you warm and even if the temperature is not that cold they work equally as well. Essentially they feel like they regulate the temperature pretty well, and given how small they are they seem to do an extremely efficient job at it.

Now before we get into the details of how they work, where did sleeping bags come from?

In 1876 an Euklisia Rug was patented by an entrepreneur called Pryce Pyrce Jones in 1876. This makes sleeping bags as we know them in the modern sense 142 years old! He later developed more of these bags and documents have shown (According to wikipedia – that he sold 60,000 of these to both the Russian army and the British army.

Although it can be argued that poorly made sleeping bags that were essentially wrapped blankets may have been around for a lot longer, this article will focus on the modern sleeping bag from the time of the Euklisia Rug until today.

So how does the modern sleeping bag work?

At first it seems really simple, your body omits heat and the sleeping bag keeps the heat inside itself and that hot air keeps your body warm. However if it was that simple sleeping bags would not have changed since the Euklisia Rug and yet that have changed consistently. Today’s sleeping bags can be waterproof, made from lighter and smaller material and even have the ability to create vapor barriers that air can pass through.

Now regardless of the change in sleeping bag the main two factors that control how they work are:

  • Heat Transfer – whereby the sleeping bag reduces the heat transfer from your body to the surrounding environment
  • Thermal Insulation – which works by both keeping your body heat inside the bag and keeping the colder air outside from getting in.

So how do sleeping bags work as such a good thermal insulator?

Essentially there is a material inside the sleeping bag covers that is either a natural material or a synthetic material. Likely the original thought behind the natural material was to use duck or goose feathers as these animals have lightweight feathers that keep them warm and are also waterproof. However it was finally found that sheep’s wool has one of the best insulators from water.


Now although natural materials have been used for most of their history, recently with scientific breakthroughs of materials science, synthetic material appears to outperform natural materials. The materials can rang from Polarguard to Thermolite, to others but at the end of the day they are lighter, better insulators and temperature regulators and also better at resisting water. Only issue with synthetic material is that it is usually more expensive!