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 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.
Or if you favor your high-ends, you could also take into consideration acquiring an airbed to sleep on, but if you do, guarantee it fits in your camping tent before taking it away with you. The last thing you want is to arrive at your assigned camp website and find that your resting tools is as well large. This will destroy your whole outdoor camping experience before you also make it through your first night, and also as we understand, a poor evening's rest will establish the mood for the rest of your stay. And also we don't desire that.