The cut-out at left was a failed attempt.  Starting again here. The rough-cut blank craft foam with 1/2" holes drilled to clear the screws protruding inside the visor shell. The blank protrudes front of the helmet sides. Cutting to fit inside the helmet sides. Fits inside the helmet sides now. It's going to trim nicely to meet the vinyl neck visor. Double-sided fabric tape from Walmart is extremely sticky and will create a permanent bond. Left ear with double-sided fabric tape applied, with tape backing still in place. Double-sided fabric tape around rear edge and interior. Right ear fabric-taped. Working from left ear around to right ear, remove portions of tape backing and secure padding in stages. Secure padding to left ear area before peeling backing off remaining taped areas. Sticks very well. Next remove tape backing from rear area. Showing rear area tape backing ready for peeling off. Rear taped area ready for sticking the padding to it. And finally, remove tape backing from right ear and press padding into place. Craft foam padding is now securely bonded to the vinyl neck visor. Front view of bonded padding. Side view of bonded padding. Rear view of bonded padding. Use a razor blade to rough-cut the padding. Rough cut complete. Be very precise, and with a short cutting action, use the vinyl as the blade's guide. Use a sliver of a razor blade to navigate the tight curves of the ear areas. Final cut of the neck padding complete. Looks good, but blade leaves a lot of cut marks on the padding. Use 320 grit sandpaper on craft foam to reduce jagged cut lines. Final neck visor looks really good.  The vinyl backing will stand the test of time over craft foam alone.