Your heat retention (fill power) takes into account that you’ll be wearing something underneath, such as a layer of clothes. If you’re not sure what temperature ranges will drop to at night (especially if you like to go remote camping), you’re always supposed to plan for the worst-case scenario. Pack and wear thermals under your jacket to push that heat retention even further.
We personally recommend this set to keep you warm as possible. Down jackets are the perfect addition to your camping and hiking gear to maintain your body temperature out in the wilderness, but they can’t do all the legwork. I learned this the hard way when I first dealt with chilly weather outside of Texas. Layers underneath are the key to warmth.