Swix HS is a hydrocarbon based ski wax with dirt repelling and gliding additives made for training and racing. Swix has been making wax since 1946 and is the world leading ski wax brand. 

Swix HS is some of the best price-for-performance ski wax for cross country and skimo racing. 

If you're uncertain about which wax you need, typically you'll only need HS8 (Red), HS6 (Blue) for most of the season and for parts of the spring. For warmer days in spring and for waxing your skins, having a bar of HS10 (yellow) on hand will cover you for warmer days. 

If you're uncertain about which wax to use, it's a safe bet to err on the side of colder wax, as it will be more durable and resist dirt better.