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.
Think about the time of year you will certainly be going and also whether or not the nights will certainly be chilly when you're heading off outdoor camping. Take into consideration whether you really feel warm or cold when you sleep. If you feel the cool, you might want to think of a camping mat to sleep on which will certainly protect you from the chilly night ground and also supply you with added warmth. It's much easier to unzip a sleeping bag and cool off if you are feeling warm, than it is to get rid of the cold.
The other sacrifice is the size or thickness of the bag. A mummy sleeping bag essentially will certainly be much smaller sized for bring around which is why it is a preference for many backpackers/hikers. The rectangular resting bag isn't as small yet because it's not common to be lugging it, apart from somewhere in a vehicle while getting to your intended location, the bulkiness of the bag is not as large a problem.