I have a mix of brands including Craft, Wickers, Jockey, they're all polyprop and they all work fine. The price varies a bit but the quality and performance is fine for all of them. X2 on the Doo Socks, just one layer, one pair, all day and my feet are warm throughout. I wouldn't have guessed that a simple sock could make that much of a difference.
How polypropylene keeps you warm and dry.
The key to effective dressing in cold weather is layering. Your body has its own heating and cooling system; layering can maximize the efficiency of your body system and allow adjustment to various levels of exertion so you can maintain a comfortable temperature. Polypropylene thermals should be the first undergarment next to your skin. This is the most critical layer to ensure warmth. When participating in outdoor activities you will inevitably begin to sweat; sweating is your body’s way of cooling itself. Cooling is good during warm summer sports, but in cold weather it can actually work against you. Your next-to-skin layer or underwear should be made of a material that will pull the sweat from your body keeping your skin dry and comfortable. The process of pulling sweat from your skin is often referred to as “wicking.” Underwear designed to wick come in an array of materials, some natural and some synthetic. Polypropylene is a superior fabric to others such as cotton. Cotton and many other fabrics wick sweat, but retain it and take too long to dry, keeping your skin wet and cold. Polypropylene underwear does not absorb any moisture so it dries very quickly. 100% polypropylene is not only the best in terms of performance it is also the best value.