Spider silk
A protein fiber spun by spiders; its very high tensile strength relative to weight makes it a target of advanced materials research.
The strongest known biological material isn't spider silk but limpet teeth. Measured in 2015 at 3.0–6.5 GPa strength, they beat spider silk (~4.5 GPa). Scraping algae off rock, they embed goethite fibres in soft protein, tough at any size.
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