I have long, thin, straight hair which I lighten to blonde. Because of this I try not to wash it more than once or twice a week to prevent it from drying out.
Tresemme Waterless Foam Shampoo is great for those days when i wake up late and realize that i probably should have washed my hair the night before.
I wouldn't recommend it for regular use, but it sure is a lifesaver in a pinch!
You just spray it on, wait a few minutes and then brush it out.
Usually it's only the back of my hair that might get greasy so i'll just spray that part.
It doesn't give you the same feel as freshly washed hair, but it definitely keeps it from looking greasy.
I would recommend having a can of this around for emergencies :)
It's also great for camping! :)