User Review: The North Face Bighorn
Design: modified mummy
Temperature Rating: 20F
Weight: heavier than advertised
Price Paid: $90
Believing the temperature ratings on a North Face bag can be hazardous to your health. This bag is rated 20F. It will probably be okay at 40F, but you could get in serious trouble at 20F.
North Face is very tight lipped about exactly what the H.O.T. insulation used in this bag is. But you shouldn't be too concerned because there is almost no insulation in the bag.
The bottom line on sleeping bag warmth is loft--how thick the insulation layer over you is. I test any bag's insulation by putting one hand inside the bag, and the other outside. I then try to lightly touch my fingers together to get a sense of how thick the insulation is. On this bag my fingers touch like there is nothing there, so the fact that it works down to 40F is fairly miraculous.
Once upon a time North Face made good gear, but for quite some time now their business model has been based on catering to urban fashion horses. It is possible to initiate the vicious cycle of hypothermia in temperatures as high as 50F. Add water, fatigue, and hunger, and it could be your last night out.
I bought this bag by mail, and kept it only because it is large enough to serve as a shell for another bag. A two bag system is quite versatile.