I own a pair of the Surge model FiveFingers, the direct predecessor (now discontinued) to these shoes. They are my only (so far) pair of FiveFingers; I bought them specifically for the warmth and protection of the Neoprene fabric.

To specifically comment on the Neoprene, it definetly keeps your feet warm in cooler weather. As long as my feet stayed dry, I could withstand temperatures down to 14?F, though for comfort I wouldn't go much cooler than 25?F. However, temperatures in the 50?Fs were too warm for my feet and I actually sweated through the Neoprene! This is because the FiveFingers make you walk in a natural manner, causing you to use all your foot muscles, thus giving them a great workout which means lots of generated heat.

This week its been in the 20's through 40'sF and I have been wearing my Surges in snow and through puddles. The combined insulation of the Neoprene and heat from my own feet was plenty to keep my feet from freezing.

I am looking forward to ordering some KSOs to complement my Surges for warmer weather. :)