Why aren’t these tights waterproof?
                            Waterproof membranes have the disadvantage of not being very breathable. However, cross-country skiing is an activity that requires intense physical exertion. The risk would therefore be to sweat a lot, and then get cold.
That’s why for your cross-country ski outfit, the materials used are water-repellent (water slides off the material) and not waterproof. 
Waterproof clothing is only recommended in heavy rain or snow when you are outdoors.
                           
                                                  
                            How to stay warm and dry during my cross-country skiing outings?
                            These tights cover a wide temperature range, so that they can be worn for an extended part of the season. 
If it is very cold, you can add a technical breathable base layer under or over windproof over-trousers. This three-layer technique also depends on each person’s sensitivity level to the cold.
                           
                                                  
                            Why should you protect yourself from the wind?
                            Did you know that the wind makes you feel colder? 
With an outside temperature of 0°C and 20km/h winds, it will feel like the temperature is -10°.
So-called "windproof" components help to reduce this windchill by blocking the air flow resulting from the true wind and the forward motion of your sporting activity.