Synthetics are every bit capable as down to insulate @ 20 degrees. I can keep you warm with snow, steel wool, theater popcorn or 1000 remaindered copies of Rod McKuen 'poetry' books. Obviously though some materials better lend themselves to our task. Insulation ratings are always optimistic. The bag is inside of a tent with the occupant wearing additional clothing. If you've read Jerry's (in) famous newsletters the shortcomings of other insulators are explained. First and foremost many have a relatively short life due to fill breakdown from use, washing or compression, AKA loss of loft or 'going flat.' If you only go camping a few times a year, the unit seems to last years. But if your out there daily the actual lifetime can be mere days . If you can trade this off for an adequate bag solely for emergency car use then cheaper bags will work. Just remember that kept compressed there will loss of insulation. Many materials require considerable time ( and vigorous shaking) to regain even a % of rated loft. This is an emergency bag, and, given the restricted parameters there are numerous units more than adequate. We need your fiance emerging crysalis like from his car after the blizzard passes or rescue comes, not assaulting the polar caps on snowshoes. Just eliminate the scary stuff Wiggy discusses, get the lowest rating you can afford and don't forget what else keeps a body warm; food, liquids, chemical warming packs.