Originally Posted by old4hats
About what temps will this be effective down to, or a best guess.
Generally speaking, most folks can use a regular poncho liner down into the low 50s or high 40s as top insulation. A footbox might extend that by another three to five degrees.
Personally, I'm good down to the high-thirties (and can use it as low as freezing, as long as I don't mind being chilly all night) without supplemental insulation, but I'm a space heater.