This variant of The Jerven bag was earlier developed upon a wish from the Military: «Make a Jerven bag, which is warm enough to replace the sleeping bag at winter time.»
Well, some think we have succeeded, others don’t. We have gotten feedback from avid open-air campers,who seem to be able to take the most of what you might throw at them of low temperatures. Ohers shiver when the night temperatures get close to + 5º C (41°F.). Ifyou use a light sleeping bag in addition, you ought to do just fine.
As a windsack it is quite superior. When you sit in this bag, it is close to impossible to get under + 20º C (68°F.) ! About 25 degrees C (77°F) is common. (See the Sintef report.) But, then you’re awake. It will not be quite the same when you sleep. You will fall asleep, but you may also wake up rather early. Most of us are very spoiled with the comfortable quilt at home. In any case, it is a definite alternative to the sleeping bag.
As wind sack/bag the The Jerven bag, Thermo Extreme is 2,2 x 1 meters. The padding is PrimaLoft 170 grams (0.4 lbs) per m². All the other thermo canvasses have PrimaLoft 60 grams per m².