Just the Heat Pad Only! This fascinating hands-on experiment utilizes a 7.5" x 7.5" pouch of supercooled sodium acetate to visually demonstrate crystallization and the subsequent release of latent heat. Indefinitely repeatable, simply boil and cool the pouch to return its contents to the supercooled state. Best of all, you can use it to introduce conservation of energy to students of all ages.Size: 7.5x7.5 in. Download the MSDS sheet.