[ROUSHAC]

Lots of good recommendations above, but if it still fogs up, try this quick trick that one of the instructors told me about at Mid Ohio.

Get a small piece of soft foam insulation about 1/4" thick, 1'4" wide, and about 1 1/2" long with the sticky backing on one side.

Place it in the middle of the lower opening for the face shield so that it goes from the outside of the helmet across the opening to slightly inside the helmet.

You are then able to open the face shield if if it starts fogging up, close it back to an "almost" closed position where it will remain, and if you push the face shield a bit harder it will go back to the "locked" closed position.