Best for very cold days
I have a couple different thicknesses of Icebreaker Ski Socks. They are all the SKI+ model, meaning there is a left and right so no extra bulk bunches up inside your arch. The Ultralights are perfect when I race but if I'm just out skiing groomers on a really cold day, the SKI+ Medium offers a lot more warmth. It does take up a little more room in my boot but it's not hugely bulky. Very warm and comfy.