If you fold it over and let it run for a bit or put another blanket over top to retain the heat, they really work well. They will be going with you on all future cold weather camping trips.
Be careful that you UNPLUG it if your car isn't running, as it WILL DRAIN YOUR CAR BATTERY if you leave it plugged in overnight!
Name: 12 Volt Car Use Electric Blanket, Buy Outdoor Heated Blanket, Heating Blanket for Car Use
Material: Semi cozy fleece(Polyester)
Plug into the cigarette lighter socket
Automatic temperature control
Cigarette plug with safety fuse