MERIWOOLMerino Wool Hiking Socks for Men and Women – 3 Pairs Midweight Cushioned – Warm, Breathable

Q: it says 75% wool, and 100% wool.. which is it? if it's 75%, what are the other fibers?

It is 75% wool, merino wool. The 100% you read is that the wool they use comes exclusively from the merino breed of sheep. Just like dogs have coats that feel different (think short haired dachshund vs cocker spaniel), so do different breeds of sheep. They use 100% merino wool but it only makes up 75% of the fiber content.

Q: Are these socks good for sweaty feet that sweat more in the winter?

Wool is good for wicking moisture away from skin. However, inside of a waterproof winter boots, there's a limit to the wicking. YMMV

Q: What weight would you say these are- Light, medium, heavy?

medium+, might stretch your everyday shoes. i am looking for ultra light i guess to avoid stretching my everyday runners. 2nd day wearing. but they seem solid.