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.
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.
Prior to establishing your backpacking bag, be sure you shake it out a number of times. This will certainly help "fluff" it up and also increase the airspace. If your bag includes pockets, be cautious with simply what you determine to put in them. Prior to buying the bag, take note of the pockets different places.