So I tested Icefalcon Armory's 1/2" helm padding in my 1/2" clearance helm. Our Province Marshal hit me three times with a Light(3), Normal(5), & Hard(7) power level. By Normal(5) I was not happy and Hard(7) made me really uncomfortable & hurt. I did not ever want to be hit with a single handed sword at Hard(7).
It may be good for padding if you also have some softer stuff there (IE; multi-layer padding), but for primary use? Not so much. As an SCA Combat Marshal I'd not recommend it.
For reference: My old padding, which was smurf blubber & Windrose EVA, didn't feel like this. I used it for many years before deciding to replace the stuff in case it had aged out. My helm weighs 13lbs. It's a Windrose MTO Norman with a riveted aventail.