Sleeping bags are all about comfort, right? I mean, we talk about liquid capacity and versatility of hydration packs, weight, and durability of backpacks, and size and weight limit of hammocks, but we like to talk solely about comfort when it comes to sleeping bags.
One very large comfort factor of camping is how warm you are in and out of the bag. So that is what we'll focus on for this quick guide.
Understanding the Standards of Temperature Ratings
When shopping for, or researching, your next (or first) sleeping bag, you'll notice that they always have a temperature or set of temperatures associated with it. These temperatures indicate the lowest temperature at which the sleeping bag should keep a person warm.
For example, a sleeping bag rated at 35 degrees F should keep a typical person warm at temperatures of 35 degrees and higher (warmer).
Please note, this rating is measured with a few factors. It assumes that the person in the sleeping bag is wearing a pair of long underwear and with a decent quality sleeping pad under them. (Sleeping bags form an insulation barrier between the cold ground preventing it from sapping body heat)
Here's the thing, though, sleeping bag insulation and ratings vary from brand to brand and make to make. Also, the rating does not take into account the large variances in everyone's metabolism.
How Does Metabolism Affect Body Temperature
Your metabolism is essentially how fast you burn calories. Thus, a person with a higher metabolism will be warmer inside of a sleeping bag.
However, people's metabolism at a resting or normal rate can vary greatly, so a sleeping bag that is fine for one person, maybe freezing for another.
People who work out or exercise increase their metabolism and the body gets warmer and sweats.
Sleeping Bag Temperature Ratings and What They Mean
Sleeping bags are usually divided into three main categories - Summer, 3-Season, and 4-Season/Winter.
Summer Season Sleeping Bags
These are usually rated for anything above freezing so +32 degrees Fahrenheit (0 degrees Celsius) and warmer (higher)
Example: TETON Sports Journey 35+ F Ultralight Sleeping Bag
3-Season Sleeping Bags
These are rated for use from around 10 degrees Fahrenheit (-12 degrees Celsius) but can get a bit too warm in summer
Example: GEERTOP® Comfort Lightweight Envelope Sleeping Bag
4-Season/Winter Sleeping Bags
These things are rated for +10 degrees Fahrenheit (-12 degrees celsius) and colder (lower) but how much lower will depend on the model. If the ambient temperature gets above freezing, you will normally roast in these, so they are not much use outside of really cold climates.
Example: TETON Sports Celsius XL