The Over bag is a +35 degrees F (approximately +5 degrees C) rated mummy style bag that can be used to create the FTRSS system, lowering the certified temperature rating of a bag by -40 degrees F. It is available in four sizes. Please note the larger size for the over bag, so it will fit comfortably over any of the other bags when the FTRSS is created. Also note that a larger roomier bag is necessary for warm weather use.