If you ever fancied mounting - 'fern root', coir, filter (synthetic) sponge and natural sponge are great for the wire like thin roots. Moss is definetly an extreme at one end of the scale and I would have to stay far away from it and go towards the other end and use bark. Highly dependant on your care approach, temps, airflow etc. If anything you dont want epiphyte orchids standing with their roots saturated for any length of time. Throw cool/cold temps in and its a goner!