When you are looking through a manufacturers catalogue you will notice that most include sleeping bag temperature ratings. There is no standard way to calculate a temperature rating for sleeping bags but a number of parameters always come into play when it comes to having a warm sleep. Ratings are determined by the manufacturer.>
Factors In Sleeping Bag Temperature Ratings
- Loft or thickness of the sleeping bag. The thicker or "fluffier" the sleeping bag the warmer it will be.
- Hooded bag or hoodless. Adding a good hood to a sleeping bag aids greatly in its temperature rating
- Is the bag snug or roomy? The less air space in the sleeping bag, the less you have to heat with your body.
- How does the bag control drafts? Sleeping bag zippers and seams leak cold air like a sieve. There needs to be some way of blocking this cold air from entering your sleep space.
- Type of insulation material and quality Insulation construction.
- Methods used in the sleeping bag construction include baffled, sewn-through, and shingled.
- Permeability of air through the shell of the sleeping bag. Even a small breeze can bring the percieved wind chill temperature lower. Wind can increase the amount of cold air that penetrates the material of the sleeping bag and carry away heat you have generated.
Other Factors of Warm Sleep In addition to the sleeping bag itself, other factors that cannot easily be quantified must be considered when calculating the warmth of a sleeping bag.
Factors that may affect the temperature comfort zone of your sleeping bag are many and varied. Every person is different and conditions of both the individual and the environment differ at any given time. Airs relative humidity can effect warmth comfort.
One night you may feel warmer than another night. Perhaps you are physically stressed from a strenuous day, lack of food or dehydration. Perhaps there is a stiff wind blowing or your bag is a little damp. Some people sleep cold, others hot. Men tend to produce more body heat than women, and a male’s body mass tends to be higher than that of a female and so tends to cool down more slowly.
Using Loft to Calculate Sleeping Bag Ratings There is no clear-cut way to determine the temperature rating of a sleeping bag for each individual and every environment. However, loft is a good starting point from which to calculate the warmth of a sleeping bag without actually testing it in the field.
In addition to loft, there are key performance features we can use to estimate the relative temperature rating of a sleeping bag as compared to other makes and models.
As a general rule of thumb, for a good mummy type bag from a reputable dealer, with insulated hood, drawstring, and draft collar at the zipper, well sewn with no exposed seams etc, when the temperature is below freezing you can expect about 10 degrees F of warmth for every one half inch of insulation above you. Insulation that is compressed underneath you is next to useless and so does not count.
If you have any additional questions regarding sleeping bag temperature ratings please contact us!