I am not familiar with the comic book, but I did know about the character a bit and I have seen the movie. In the movie it's never said directly what the role of the suit is exactly. At one point, they make it seem that the suit is vital and then at another point it seems it is not.
What I am referring to is to a few different scenes in the movie. One is the scene with the goat, which obviously was not wearing a suit, although it was in a glass container. My understanding of the Pym Particle is the shrinking effect takes place when the particle is released in a gas. This would explain the suit and the glass container with the goat. It also explains the demise of Yellowjacket at the end of the movie: as the circuits are destroyed it seems the suit is flooded with the particle in uneven amounts, causing his body to become mangled when it shrinks at various rates in different places.
But then what about the little throwing stars that he uses to shrink or enlarge things? It does look like there is a glass cylinder in the center which contains the particle, but are we to believe that upon breaking open the gas automatically covers the object evenly, allowing the item to enlarge or shrink without being mangled? And if that is somehow possible, why do they make it a point to have the scene with Hank in the back of the police car? They show him knock the suit onto the seat and struggle to position his head and the second the helmet appears to make a seal he shrinks? So is the suit needed or not?
Also I read that in one issue of the comic he accidentally shrinks Spider-Man. So what is the purpose of the suit? It seems unnecessary??