Pinlock: https://pinlock.com/products/lenses/
It's a thin piece of plastic that fits on the inside your regular visor. It has a small band of silicone around the edge, so that it seals completely to the visor, trapping a layer of air between the visor and the Pinlock. It effectively creates a double visor like you might see on a snowmobile helmet. It uses two "pins" through the outer visor to hold the pinlock in place and adjust the tension to maintain an airtight fit.
Most Shoei and Arai helmets now come with a Pinlock in the box.
It's a thin piece of plastic that fits on the inside your regular visor. It has a small band of silicone around the edge, so that it seals completely to the visor, trapping a layer of air between the visor and the Pinlock. It effectively creates a double visor like you might see on a snowmobile helmet. It uses two "pins" through the outer visor to hold the pinlock in place and adjust the tension to maintain an airtight fit.
Most Shoei and Arai helmets now come with a Pinlock in the box.