Works well under helmet, but I wouldn't use it under 20 degrees snowmobiling. the top is mad of thin nylon which gets really cold when wind/helmet breeze hits it. the bottom face mask part is made of fleece which works really well .
I typically have problems finding a head sock/balaclava that fits my head well. This one fits well, is comfortable and warm. Probably could find something of similar quality at a few other places, maybe slightly cheaper, but I am satisfied with the product.
The fit of this product is very contouring to the face and neck, which is perfect for under a helmet. Its longer, so you can tuck it into your jacket or sweatshirt and keep the cold off your neck! Very durable product. Can wash but do not out in the dryer. Hang it up to dry. Great Product!