I've now used this bivvy bag in high altitude wilderness settings several times and it works. Summertime high CA Sierra forest gets about 45f at night and i was still warm in this bag. I realize this bag is of confined space inside to reduce the amount of air your body has to heat but im a big guy. 6'5" 233 lbs and would like a bit more room at the top to move my arms a bit for comfort. The only thing i don't like about this bag is the width of the top for shoulder room. And since i use this bag recreational I'd like another color. I think Adventure Medical doesn't ABSOLUTELY have to stick to the "emergency" aspect of use. Its a fine product so get more customers by offering sises for bigger or smaller people and other colors. If you cant put more room in the top of this bag because of air heating issues, then what about all that space in the bottom when used by a short person. This fine bag is perfect for John Q Normal. Great idea anyway.
Adventure Medical Kits Sales Rep and Professional Adventure Racer Kyle Peter breaks down the Survive Outdoors Longer® Escape™ Bivvy, the first breathable heat-reflective emergency shelter. More versatile than any other emergency shelter on the market, the Escape is a true crossover, good even as a replacement sleeping bag in temperatures down to 50 degrees.