Or just avoid said armor of course. But that's complicated. It's mostly useful against back-stabs. 

Contrary to its size and weight, spider silk is naturally capable of absorbing a huge amount of energy. [url=http://news.discovery.com/tech/gear-and-gadgets/body-armor-spider-silk-121015.htm ]Spider silk[/url] has a natural stress distribution when struck btw, since you asked how it adsorbed energy from a blow.