Niagra Fabric Finish Spray provides a smooth finish to fabrics and allows the iron to glide easily. It's a great for heavy-weight fabrics like linens, jeans and cottons. It's not a true starch but it gives more body and crispness to fabrics and certainly makes wrinkle prone shirts look much nicer. The same manufacturer makes a spray starch as well if that is your preference. Needless to say, I am a changed man, at least when it comes to my ironing.
On a side note, this product does not contain chlorofluorocarbons (CFCs) which, along with other chlorine and bromine containing compounds, have been implicated in the accelerated depletion of ozone in the Earth's stratosphere according to the Center for International Earth Science Information Network (CIESIN), the Environmental Protection Agency and other reputable organizations.