Piloerection & lymphatic constriction
Cold water prep will result in piloerection (the whisker stands up) and constriction of the lymphatic capillaries. This constriction will cause the tissue to recede from the base of the whisker (making the hair seem longer) as well as reduce fluid loss in the event of a nick or cut. Capillary constriction from cold water will be more evident first thing in the morning when our faces tend to be puffier from having been in bed for several hours. Evening shavers may not notice as much effect assuming they’ve been semi-vertical all day.
Cold water will also affect the way fats and oils lay on and/or are absorbed by the skin.
Hair is expanded (softened) by the absorption of water. The conventional wisdom is that soap allows more water to be absorbed- something about surface tension or its hygrophylic properties. I’m not sure if the temperature of the water makes a lick of difference.
Or maybe I just made all that up.
Semper circa,
LG Roy