Heavy cushion ski socks are a solid choice if you run cold or ski in extreme conditions. The thick padding throughout the foot and leg provides maximum warmth and impact protection, which is especially helpful for beginners dealing with boot pressure or anyone wearing rental boots with extra room to fill.
That said, heavy cushion isn't always the answer for cold feet. If your boots fit snugly, all that extra padding can actually make them too tight, restricting circulation and making your feet colder—not warmer. You'll also lose some of the responsive boot feel that helps with precise control.
The key is matching cushioning to your boot fit. Heavy cushion works best to take up volume in looser boots. If your boots already fit well, a medium cushion with good moisture-wicking might keep you warmer overall. And never double up on socks—that just creates wrinkles and cuts off circulation, which is a fast track to freezing feet.