generally, snowmobile helmets are motorcycle helmets, but with two key differences: They include a dual lens shield and a breath box. Both of these are necessary to prevent fogging in cold environments!
Unlike motorcycle helmets, many snowmobile helmets will use fleece padding for additional warmth. Also, note that most snowmobile helmets also offer an optional electric double lens shield to reduce fogging even further than the standard dual lens.
Some motorcycle helmets can be converted to snowmobile helmets with the additional purchase of accessories from the manufacturer. The Bell Star Carbon Helmet can be converted to a Star Snow Helmet for as little as $49.95 with the purchase of a double lens shield snow kit. For a complete electric version, you can purchase the electric shield snow kit for $119.95. Either of these options will allow you to get double the usage of the helmet, but the helmet itself starts near $650.