Using superior natural fibres such as merino wool are ideal for running socks. Not only are they naturally breathable and sweat-wicking, but they're also anti-bacterial, leaving you without the stink.
Polyester and nylon are popular synthetic fibres for running socks as they're both sweat-wicking, breathable, and more durable than cotton.
Try to avoid 100% cotton socks because it holds moisture. So, if your feet get wet through sweating or rain, they'll stay wet and damp, leading to problems like chaffing and blisters.