Our warmest winter bags keep you cookin' in the mountains and polar areas, while the lightest ones serve you in indoor and hot weather use.
You are the radiator, the sleeping bag is only insulation. By keeping yourself energized and hydrated you enhance your chances of a good night's sleep.
Thankfully comparing bags is easy as they have EN tested temperature ratings. The EN test gives each bag three values: extreme, limit and comfort temperatures. You can forget about the extreme one and concentrate on the other two: for a cold sleeper, aim for the comfort temperature and for a warmer sleeper, the limit might be a better idea.
Even the warmest sleeping bag out there needs a sleeping pad - your weight will squish the loft out of the bag from under you and that loss of insulation needs to be covered by your pad.
Winter bags are often referred to as four season bags, but to be honest they tend to be too hot for use during summer.
When at all possible, it's a good idea to air your sleeping bag after every night while you're out there. This helps get rid of some of the night time moisture.
You'll get the most out of your bag by storing it in a loose roll at home. Keeping a bag in its compact bag will flatten its loft over months and years.