If you see a +20 degree score that would certainly indicate that the bag should be cozy enough for temperatures that are 20 levels or warmer.. And if you see a - 20 level score then it has actually been figured out that the bag needs to be cozy sufficient for minus 20 degree climate.
Some U.S. companies of backpacking sleeping bags have complied with the European Standard (EN 13537) technique of temperature level screening. Without entering into excessive deepness about exactly how they reach these numbers, generally they check the best sleeping bags under strict standards using a clothed dummy sporting long underwear and also a hat. Sensors on the mannequin document temperature readings.
The last greatest factor to consider in selecting a bag is the insulation that is used in that bag. While both will do the work to maintain you warm, they both have their pros as well as cons. Some kind of extra padding under the bag is very advised.