I purchased these socks to use with my Vibram Fivefingers.  I was looking for something thin enough so it wouldn't make the shoes too tight but warm enough that they'd help keep my feet warm running through fall.  I looked at other socks but they were so expensive, I just couldn't justify it.  I went out on a whim when I purchased these, but I have to say I'm very pleased.  They're comfortable, fit great, my shoes still fit great and my feet are staying warm now that it's cooler outside.  I don't think these socks would do much to protect my feet through running outside in a WI winter, but I also don't think the Fivefingers shoes were made for running in snow and ice.