Hair spray is the most common alcohol-based styling product. It is a solution of polymer in a mixture of alcohol and water that is sprayed on the hair in small droplets. The droplets are formed when the liquid is forced through a tiny pinhole in the nozzle of the can. In aerosol hairsprays, the force is supplied by pressurized gas called propellant. In non-aerosols, the force is supplied via mechanical action of pumping the nozzle. Typically, aerosol propellants provide more force than mechanical pumping, resulting in smaller droplet sizes. Smaller droplets dry faster, giving aerosol hairspray a "drier" feeling than non-aerosol hairspray.
It's a myth that alcohol in hair spray dries out your hair. First, you don't soak your hair in hairspray; you only apply a very small amount. Second, the alcohol evaporates away very quickly, without getting a chance to penetrate your hair or pulling out any water.
Alcohol-based styling polymers are delivered to the hair in a solution of polymer and alcohol that dries very quickly. The rate of drying is much faster than that for water-based styling products because alcohol evaporates much faster than water. As the alcohol evaporates the film dries, forming bonds between hair strands, welding the hairs together in the desired style. A fast drying rate makes alcohol-based stylers perfect for locking in finished styles because they do not rewet the hair.
Alcohol-based polymers are typically much more humidity resistant than water-based polymers. This is because alcohol-based polymers require surfactant, like shampoo, to make them soluble in water. Thus the water available via high humidity does not soften or loosen hairspray bonds.