Pop Rocks candy works by releasing tiny pockets of highly pressurized carbon dioxide in the candy. This carbon dioxide is infused into the hard candy during manufacturing.
Pop Rocks are similar to any other type of hard candy. Sugar, corn syrup and water are boiled until the water is completely extrapolated. After the mixture has been processed, poured out and pressurized to 600 psi in a chamber filled with carbon dioxide, the candy is allowed to harden. Because the candy is allowed to cool while still pressurized, the tiny bubbles of carbon dioxide in the hard candy are under pressure and explode when the it melts in the mouth.