Our rink puts on The Nutcracker on Ice annually. The boy playing the Prince / Nutcracker this year was waiting to step on the ice last night while holding his giant head, lol. (The Nutcracker head, not his real head.) So I took a peek...
It was filled inside with soft cushion foam from the sewing store. I think they added new foam this year since everything looked clean and tight. (Last year's skater was older and bigger)
There was an opening in the center so he could put his head inside, maybe 5" in diameter. He said he had to be careful about not squashing his ears. The face part was open, so he could see and breath, but there was a strip of foam across his brow so the head didn't move much.