About a week ago.
I was having a  discussion with a member on Private message about sleeping bag .
So I thought I should try to explain why people should not trust  ratings completely for Sleeping Bag ratings.
First thing to understand is the ratings.
Sleeping Bags have 3 temperature ratings usually.
Comfort - Comfort temperature ratings are usually should be most important. As this is the rating that most cold sleeper( people who feel more colder like woman) should be comfortable for usually 6-8 hours of sleep.
Limit - It is a temparture rating that most men( who are usually warmer) should be comfortable in. This is mostly few degrees lower than comfort level but it can still be considered.
Extreme- Now this temperature is where you need to take in lot of factors and most dangerously misunderstood.  It can cause freezing and hypothermia.
Most people see -30C extreme level rating and buy it… firstly this will only give you few hours of survival in such low temperature with many factors accounted for like your body heat producing and if you well eaten to produce that heat plus how well you are covered.
and on cheap sleeping bags this ratings should never be even considered.
A high and expensive sleeping bags like PHD, Mountain Hardwear,The North Face, Western mountaineering etc…these companies have very high reputation and that is why you can still consider their ratings as still very close to real feeling.
and Even then they mention some of the factors I mentioned. They sell their sleeping bags for $800-$1400 …so you can imagine how stritcly they follow testing and rating rules.
Rest most companies follow such basic guidelines to rate their sleeping bag.
so Please dont just see a Rs 2000 , -10C sleeping bag and this you will be fine at -10C with it.. You are only risking your life just to save some money.
weather in mountains are usually very unpredictable specially due to high winds and ground tempature .
So be safe on all your adventures and buy a good rating gear from good brand if doing some serious trekking.
Beside all above things…there is lot more like Humidity , wind , goose down or duck down, synthetic insulation …so do your research well .