The article explores the molecular mechanisms behind the toughness of natural adhesives, fibres, and composites, focusing on spider dragline silk and abalone shell nacre. Spider silk is noted for its exceptional strength, while abalone shell nacre is 3,000 times more fracture-resistant than pure calcium carbonate. The key to nacre's toughness is attributed to the organic adhesive, which holds the calcium carbonate plates together. Using atomic force microscopy, the authors reveal that the adhesive fibres elongate in a stepwise manner as folded domains or loops are pulled open, with elongation events occurring at forces of a few hundred piconewtons, much smaller than the forces required to break the polymer backbone. This 'modular' elongation mechanism is suggested to be a general principle for enhancing toughness in natural fibres and adhesives, potentially applicable to spider silk as well. The study also discusses the modular structure of lustrin A, a protein found in the abalone shell, and its role in the adhesive properties. The authors compare the force-extension curves of different materials, highlighting how a material with intermediate-strength bonds can combine high strength and high toughness.The article explores the molecular mechanisms behind the toughness of natural adhesives, fibres, and composites, focusing on spider dragline silk and abalone shell nacre. Spider silk is noted for its exceptional strength, while abalone shell nacre is 3,000 times more fracture-resistant than pure calcium carbonate. The key to nacre's toughness is attributed to the organic adhesive, which holds the calcium carbonate plates together. Using atomic force microscopy, the authors reveal that the adhesive fibres elongate in a stepwise manner as folded domains or loops are pulled open, with elongation events occurring at forces of a few hundred piconewtons, much smaller than the forces required to break the polymer backbone. This 'modular' elongation mechanism is suggested to be a general principle for enhancing toughness in natural fibres and adhesives, potentially applicable to spider silk as well. The study also discusses the modular structure of lustrin A, a protein found in the abalone shell, and its role in the adhesive properties. The authors compare the force-extension curves of different materials, highlighting how a material with intermediate-strength bonds can combine high strength and high toughness.