What is cake flour, and what is it used for?

Cake flour is a “soft” wheat flour which is defined by its protein content and  its very fine particle size.  It is only 5-8% protein and has a high starch content; therefore, it has weak gluten-forming potential.  It makes very light, fine-textured products.  It is bleached, usually with chlorine, so it is very white and makes very white products.  Cake flour is best used for cakes and other fragile products.  The “best by” date for cake flour is 18 months after manufacture. 
 
Source(s):
wheatfoods.org. “Difference in Wheat Flours.”