Spider silks are some of the toughest materials known to man--pound for pound, they're stronger than steel, and their webs can stand up to gusts of wind and catch hurtling insects without falling to pieces.
The silks get their strength from thin crystal proteins only nanometers wide, which are stacked together like pancakes. On the atomic level, the layers are joined together by hydrogen bonds. Those bonds actually aren't particularly strong, but that turns out to be an advantage, because they can easily pull apart and reform, allowing the silk to stretch and flex under pressure instead of snapping like a twig.
In February, Italian scientists found what they think is the stretchiest silk yet in the egg sac of the European cave spider, Meta menardi--which also just so happens to be the European Society of Arachnology's 2012 Spider of the Year. Call that one a win for animal nanotechnology.