Due to extremely cold and strong winds expected on Aconcagua (specially on summit day where we can have less than -25/-30°C with bad weather conditions) we strongly recommend the use of the warmest boots as possible: plastic or synthetic double or triple boots, just to prevent any frozen toe.
We recommend to wear boots with inner liner in order to guarantee proper foot insulation. This will give you the chance to remove and more importantly dry out by: exposing it to the sunlight (if time and weather allow it) or placing the liner inside the sleeping bag.
Leather mountaineering boots are not enough for Aconcagua summit day. The leather gets frozen and rigid at the high camps and is so cold up there that you can´t take any risk with your feet. Thats the reason because we higly recommend double plastic or synthetic boots.