Product review (5 stars): Great
This is expensive but necessary and we love the humidifier we use it with.  We didn't do anything special to it other than try really hard not to let it ever get dry.  Every time the water ran out at night and the humidifier shut off, drying the filter, there was an odd smell for a few days after.  Keep this wet at all times and I really think it lasts a whole winter.