A good night’s sleep can make or break a trip. Spending some time understanding the ratings, fill and shape of your bag could make all the difference.
Understanding Temperature ratings
· An “ISO” (International Standards Organization) or “EN” (European Norm) is a lab-tested standard of sleeping bags. It indicates the temperature rating that one can reliably compare between any two sleeping bags.
· With ISO/EN testing, a bag is assigned two temperature ratings: "comfort" and "limit" ratings.
If a temperature rating leaves out the term “comfort” or “limit,” then it's likely a brand’s estimate, not an ISO or EN test result.
· A temperature rating is not a guarantee of warmth for any bag due to numerous variables, which a lab test cannot take into account.
· Temperature ratings are estimates.
· Comfort rating indicates the temperature at which a cold sleeper might feel comfortable. This is the temperature rating brands use on women’s bags.
· Lower Limit (which is always lower than the comfort rating): indicates the temperature at which a warm sleeper might still feel comfortable. This is the temperature rating brands use on men’s bags. Based on a 'standard man' as the lowest temperature to have a comfortable night’s sleep.
· Extreme: The minimum temperature at which a standard female can remain for six hours without the risk of death from hypothermia (though frostbite is still possible).
Ratings are based on a user wearing one long thermal underwear layer and a beanie, and sleeping on a single 2.5 cm think foam pad.
Down Versus Synthetic Fill
Down
Lighter weight for the same temperature rating
Does not insulate as well when wet
Highly compressible. Small pack size
Durable
Expensive
Synthetic
Machine washable and quick-drying
Insulates better when wet
Larger pack size
Cheaper
Understanding Loft / Loft Power
This number represents the volume in cubic centimetres of a single gram of down, when fully lofted - i.e. when fully 'fluffed up'. Higher quality down (e.g. 900 fill) traps more insulating air pockets between its fine filaments than a down of a lower quality (e.g. 550 fill), and that's why it expands to take up more space per gram. The more insulating air pockets down traps, the warmer it will keep you! So in simple terms, the higher the fill power of a down jacket or sleeping bag, the warmer it will be for its weight.
Shape
Mummy
In order to boost warmth and reduce weight, this type of bag has a slim cut, along with a contoured hood you can cinch tight for greater warmth. Overall fit is snug—you typically roll over with your bag rather than inside of it.
Semi rectangular
Also known as a “modified mummy” or “barrel” shape, this designation covers a variety of shapes, all of which offer a compromise between warmth and roominess.
Rectangular
A lot of camping bags have a simple rectangular shape that maximizes roominess.
How sleeping bag shape affects warmth:
Sleeping bags keep you warm by retaining heat emitted by your body, which can warm a small space up more efficiently than an expansive space. So, a bag with a sleek shape and a snug fit will be lighter than a similar bag that’s nice and roomy.
Now that we understand the science behind it all, consider where you are going, check the average temperatures and if on a multi-day trip consider size and weight.
Sources: https://www.webtogs.com/en-ZA, https://www.rei.com/, https://www.firstascent.co.za/, https://www.rei.com/blog/camp/understanding-sleeping-bag-temperature-ratings
Written by: Shane Anderson
Team Adventure Lifestyles