Gelatin is a protein that is made using the skin or bones of animals boiled down to water, and it's not expensive.

Gelatin is a mixture of water-soluble proteins, skin, ligaments, tendons in the collagen by acid or alkali partial hydrolysis or boiled in water and produced, colorless or slightly yellowish transparent brittle flakes or coarse powder, dissolved in water at 35 ~ 40 ℃ to form a gel (water content of 5 to 10 times its own weight). Is nutritionally incomplete protein, lack of certain essential amino acids, especially tryptophan, widely used in food and the production of adhesives, photographic negatives, filters and so on.