I commute to below 0degF but not much colder than that. The main problem for me below 0 is my face and eyes. I wear a beanie and balaclava under my helmet but I almost need a full face helmet and shield and feel that's too much and opt not to go colder than that. For clothing, I use dry tech wicking under shirts in layers as needed and my regular breathable, soft shell cycling jacket. I wear windfront tights with padded cycling shorts underneath. Merino Wool socks and waterproof hiking boots or sorels, snowmobile mittens or ski gloves as needed.