I was just reading this answer at Can you keep your feet warm in ski boots on a very cold day?
Yes, add fat to your feet. I don't mean gain weight. Just slather it on before putting socks on. Petroleum jelly will work, as will almost any other fat (other than coconut oil). A nice layer of fat, even external, does wonders for heat retention.
Ignoring the ick factor that is mentioned in some of the comments to the answer. From a physical perspective what are the pros and cons of using Petroleum jelly or some other grease on your booted feet when out doors? I want to know about impacts to foot health as well as impact to socks and boots.