Not on the side of the helmet it will fracture as its unsupported.
Easiest way I can think to describe it take 2 identical sheets of polystyrene 1 inch thick. Take the first one and hold it by the edges, now get someone to start pushing in the middle of the sheet with 2 fingers. It won't take much to snap the sheet in 2 as it is not able to absorb much energy. Now take the 2nd sheet and hold it firmly against a wall and get someone to punch it. It won't break as it is fully supported, and it will deform, It has absorbed far more energy than the first sheet without fracturing. Polystyrene is good at absorbing energy when it is fully supported and it is a blunt impact, the only time you'll get this with a helmet is if you land on top of your head. If you land on the side of it chances are the helmet will just fracture.