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Chris10
10-29-2013, 18:54
I know there are a lot of variables to this, but how do manufactures come up with the degree ratings for sleeping bags. For example, wouldn't a 40 degree bag be warmer, or maybe less cooler, than the same bag using a ground pad? So would the rating be slightly higher using a ground pad?

jeffmeh
10-29-2013, 19:18
Ground insulation is necessary in all but the warmest temperatures. Where one's body compresses the bag's loft below, the bag's insulating properties are greatly reduced. Generally, the rating assumes adequate ground insulation.

There are standards for sleeping bag ratings, but not all manufacturer's hold to them. It is highly recommended to read some reviews of the bag and try to find someone who has used it at or below the rated temperature. Also note that the rating can indicate the lowest temperature at which you can make it through the night without hypothermia setting in, not necessarily a temperature at which you would be comfortable.

johnnybgood
10-29-2013, 19:28
The degree of warmth added would be the result of insulation between you and the ground surface outside your bag not the bag itself

moldy
10-29-2013, 20:41
They make it up. Nothing scientific is done to figure out what it means to buy a 20 degree bag. We humans have too much variation in body heat generation and retention. Many hikers suggest that the rating is the temp where you freeze to death.

MuddyWaters
10-29-2013, 21:19
With high quality down, its usually based on loft height, or oz of fill.
1.5" = 40f
2" = 30F
2.5" = 20F
etc.

Many commercial mfgs will have thier products EN tested. It doesnt mean its correct for any one, but at least its relative to others.

the EN testing procedure puts a dummy inside, with temp probes attached, with a certain heating rate, on a certain rated pad, and measures temperatures. Its expensive, but more and more are doing it.

And as was said, cheap mfgs will just make it up.