Product Number: SB47058
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Grades K-12. Contains a super saturated solution of water and sodium acetate. Snapping the metal disc creates a chain reaction, causing the solution to crystallize. The crystallization process gives off heat. Packs can be recharged back to the liquid state by immersing in boiling water for 10-15 minutes and allow it to slowly cool. Includes teacher’s guide. 4 in. x 4 in.