Many of your rides with booties are in cool but not brutally cold conditions maybe with wet roads or some rain and of course you always want to be aero and fast thats the thinking behind the castelli aero nano overshoe aerodynamic for use in worldtour tts and water and windproof fabric with sealed seams to keep the water out it doesnt have any insulation so it wont cover your really cold weather rdes but its spot on for everything else the upper portion is very stretchy a silicone b