This is my understanding:
Humectants are hydrating agents. They act as moisturizers by attracting water. They add moisture and softness but do not coat or weigh down the hair like most oils and waxes do.
Some hair (like mine) love humectants and can only take a little oils. Other people’s hair love oils. Then there are some hair types that love both humectants and oils. Some hair can take pure humectants like glycerin and others (like mine) need to have the humectants mixed with other products or it does not work.
Some examples or humectants are:
Vitamin E oil (like jojoba this is not really oil)
Humectants can be derived from vegetable oils (e.g., glycerin) or can be man made (e.g., Propylene glycol).
I am sure there are some articles or threads about this.........