It seems every day I am asked by my four year old daughter some science question about a typical object that I have just taken for granted. The other day she asked me about why the stop glowed at night. Fortunately, I had just been given the answer by 3M for a project we did focusing on the science behind everyday items. The answer lies within the concept of retroreflectivity. Sound confusing? Here is a wonderfully simple little PowerPoint that will help you to better understand retroreflectivity and prepare you for the next some an inquiring young child asks you about a stop sign.