I use heavy acrylic work socks with thin polypropylene liners inside. This combination is particularly warm in winter weather. Also the acrylic stays warm when wet and is more durable than wool.

The ones I use are so old that I can't remember where I bought them. Probably a workwear store. Something like Dickies Men's High Bulk Acrylic Thermal Boot Crew Socks


Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.