Spider silk is one of the toughest biological materials known to exist. This toughness comes from a combination of strength and flexibility. While spider silk is about five times as strong as a comparable amount of steel, it is weaker than certain man-made materials, such as Kevlar.
However, spider silk can stretch by up to five times its relaxed length when under pressure, and this makes it tougher than almost every synthetic material ever created.
The strongest type of spider silk is the kind known as dragline silk, which is used as the rim and spokes in web construction. Spiders can spin up to seven different types of silk for different purposes, including capturing and immobilizing prey, protecting eggs and young, and as a method of escape.
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