I use the 3oz Flash Down Booties by WM for cold temps. I’ve been fine wearing them in my 16oz 20F zpack quilt down to 20F. I do have a coolmax liner sock on.
In the morning, I loosen the straps of my sandals so I can accommodate the puffiness of down booties. I can hike with that setup for about 10 minutes before my feet are sweating up a storm.

And I bike with my down-booties/sandals-combo a lot down to 15F temperatures.
May everyone find their foot zen.

Feels good to post again.

-Barry
-The mountains were made for Teva’s

I carry a small piece of closed cell foam cut from a Z-rest pad. It's large enough for me to sit on, so I can use it on breaks and in camp to keep my butt insulated from the cold ground or the rock I am sitting on. At night I put this sit pad inside my sleeping bag under my feet. The extra insulation helps a lot in keeping my feet warm. Dual use, so the extra ounce or so makes sense for me.

Down booties help too, of course :)

As previously mentioned, a hot water bottle and a warm hat or hood make all the difference in the world. I boil some extra water before I go to bed, dump it in a Nalgene, and toss it in the bottom of my bag. Depending on how many hours of sleep I get, it'll still be slightly warm in the morning.

Most of the time though, a beanie, or if it's really cold, a hood and beanie, will go a long way to making sure my feet aren't cold.