In my writing it is a memory material that serves two functions: to deflect shrapnel (which is still a risk in the 24th century just as it is in modern warfare--being impaled by flying debris can kill you or give you an infection just as easily as a burn wound or a shock), and to partially
absorb energy blasts. Its function in the latter regard is incomplete, though, and it is still possible to burn through it or alternately deliver a shock so powerful that it still reaches the body even though the armor may seem
to be serving its function. An imperfect defense, but still better than Starfleet's nothing.