G'day Kelly,

This bag does have a 'lower limit' of -4 degrees and a 'comfort rating' of 2 degrees. The difference between Comfort and Lower Limit is the temperature an Average Male vs an Average Female can comfortably sleep. There is a great blog to explain this better than I can here! 

Snowys do advertise the Sea to Summit range from the comfort rating rather than the lower limit.

G'day Kelly,

The general rule of thumb when choosing a sleeping bag is to go with a comfort temp rating of 5 degrees less than the lowest ambient temperature you'd expect to be in, or 10 degrees less if you are a cold sleeper.  This is to account for all the variables that come into play when you're talking about sleeping in the outdoors, which can include hydration levels, activity levels, when you last ate, etc.

I'm a hot sleeper at home, basically sleep in the nud, and would have the fan on year round if I could, but that's because I'm on a very thick latex mattress and sleep with my partner whose own body heat adds warmth to the space.
If I'm out hiking or camping solo, I'm an exceptionally cold sleeper.  I need a -10ºc bag and the Etherlight Extreme R6.3 to be comfortable on cool nights around the 0-3ºc mark.
Comfort temps are a guide, and cannot account for every single person's individual biochemistry.  The best place to start when building a sleep system is with your mat.  If you're a cold sleeper you'll probably need to look at a mat with an R-Value of 4 or more.  When the EN testing is done for sleeping bag temps, they use an R-Value 4 mat.  So if you are on a sleeping mat with a lower value, the sleeping bag comfort temps aren't as relevant.

I'd really encourage you to listen to our podcast on Sleep Systems and ratings with Sea to Summit.  There's loads and loads of info there that will help you narrow down the best mat, bag, etc for you.