Spider silk is a protein fibre or silk spun by spiders. Spiders use silk to make webs or other structures that function as adhesive traps to catch prey, to entangle and restrain prey before biting, to transmit tactile information, or as nests or cocoons to protect their offspring. They can use the silk to suspend themselves from height, to float through the air, or to glide away from predators. Most spiders vary the thickness and adhesiveness of their silk according to its use.

Fiber or fibre is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate fibers, for example carbon fiber and ultra-high-molecular-weight polyethylene.