Fir bark, fern bark, cork bark, packing peanuts and wine bottle corks all make good orchid medium because they don't absorb water readily and decomposes slowly. A little pine bark in the bonsai mix adds water retentiveness and slow release nutrients. Orchid growers use pine bark in a pinch - it breaks down too fast.
Orchid growers sometimes add a little redwood bark or cypress bark to their mixes as it lowers the Ph and decomposes slowly.
