Gels are a type of mixture involving water and solids. The most common form of a gel the students are familiar with is pudding. A gel is a mixture of water and other solid molecules. The molecules will bond together to form a sponge-like matrix, which traps the water into a multitude of separate pockets.
As the granules in gelatin are heated, water penetrates the granules and separates the chains holding them together. This causes the granules to swell and soften in a process better known as gelation
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. As the granules cool down, the chains will slowly reform and become tighter.