Pop Rocks Popping Candy...taste an explosion of flavor in your mouth original fireworks-style. You may wonder what makes Pop Rocks pop? Pop Rocks are like other hard candy made with sugar, lactose (milk sugar) corn syrup and flavoring. However, what sets Pop Rocks apart is that they are processed with Carbon Dioxide. First, all the ingredients are heated together and brought to a boiling point. Next, the hot sugar mixture is mixed with carbon dioxide gas at about 600 PSI. The carbon dioxide gas forms tiny, 600 PSI bubbles in the candy. Once the candy cools the pressure is released causing the candy to shatter into little rock size pieces, yet the candy pieces still contain the high-pressure bubbles. If you look at a piece with a magnifying glass you can see the bubbles. Put the candy in your mouth and it melts just like hard candy does. This releases the bubbles with a loud POP! What you hear and feel is the carbon dioxide gas being released from each bubble.