Spider's silk is made up of chains of amino acids. In other words, it is simply a protein (see How Food Works for details on amino acids and proteins). The two primary amino acids are glycine and alanine.
Spider silk is extremely strong -- it is about five times stronger than steel and twice as strong as Kevlar of the same weight. Spider silk also has the ability to stretch about 30-percent longer than its original length without breaking, which makes it very resilient.
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