Socks can make a huge difference, on a one day 26 mile hike I made the mistake of wearing semi synthetic PT socks with padding instead of my usual wool blend. I may as well have poured sand inside my socks as by mile 18 that day my feet were a wreck. My feet felt hot due to the desert terrain (Or so I thought). It never ocurred to me to change my socks, once I did, aside from my overall fatigue, my feet were 100% better, at least functional.
As others have said the additional weight on your feet is also an additional stressor. I personally prefer the SOLE moldable insoles on boots that need "insole assistance"