Incredibly soft, warm and confortable. The kind of stuff you don't like to get off at the end of the day (if you don't have another to put on again after taking a shower !) (and, of course,  I bought 2 pairs ...)
In very cold days, I used to wear my sailing underwear to keep warm(sinthetic fibre to get dry faster tha with cotton when splahed by a wave at sea), and I discovered that when you don't need this feature, cotton is far more confortable